Tudor and Habsburg Family Trees as of early 1513
Note, bet stands for Betrothed:

House of Tudor

King Henry VII of England (1457-1513) M. Elizabeth of York (1466-present), had issue

1. Arthur, Prince of Wales (1486-1502) M. Catherine of Aragon (1485-present), had issue​
1 A). King Arthur I of England (1502-present) bet. Isabella of Portugal (1503-present)​
1 B). Princess Elizabeth of England (1502-present) bet. Charles, Duke of Burgundy (1500-present)​
1 C). Prince Henry, Duke of Somerset (1502-present) bet. Ann de Laval (1505-present)​
2. Princess Margaret of England (1489-present) M. King James IV (1473-present), had issue​

2 A). Princess Margaret of Scotland (1507-present)​
2 B). James, Duke of Rothesay (1509-present)​
3. Prince Henry, Duke of York (1491-present) M. Anne de la Tour d'Auveregne, Countess of Auveregne (1496-present), had issue​

3 A). Henry Tudor (1512-present)​
4. Princess Mary of England (1496-present) bet. Prince Christian of Denmark (1481-present)​

House of Habsburg

Philip, Duke of Burgundy (1478-150 ) M. Queen Joanna I of Castile (1479-present), had issue

1. Eleanor of Austria (1498-present) bet. Prince John of Portugal (1502-present)​
2. Charles, Duke of Burgundy (1500-present) bet. Princess Elizabeth of England (1502-present)​
3. Isabella of Burgundy (1501-present) bet. Sigismund I of Poland (1467-present)​
4. Ferdinand of Austria (1503-present)​
5. Mary of Austria (1505-present) bet. Prince Louis of Hungary (1506-present)​
Section 11: Long Live the King!
“Not long after their Grandfather’s passing, Prince Arthur, now King Arthur, and Prince Henry would leave Ludlow and begin their journey to London. They took their tutors and household with them. Rhys ap Thomas and George Talbot, the Earl of Shrewsbury. Just before the boys entered London, they would dawn mourning clothes, and join the people of London in entering a period of mourning for the late King. Shortly after their arrival at London, they would journey to Parliament, where Arthur would officially be recognised as King of England, and where the formal Regency for the King would begin.”

- Jeanne Laurence, “The Children of Camelot”​

“Henry of York would arrive in London not long after his nephews. The Parliament would officially recognise him as Lord Protector, it was the closest Henry would ever get to becoming King, and as such he is believed to have cherished the position. Quickly rumours flooded London that Henry may try and usurp his nephews, and for good reason too. The usurpation of Richard III was within living memory, and many feared that it may happen again. Of course, this would not happen, and the reign and regency of King Arthur would begin smoothly. Quickly Henry began making grants to his close friend, Charles Brandon.”

- J.J. Smith, “The Bold Prince: Henry, Duke of York”​

“The members of the Privy Chamber would remain the same, as Henry VII had requested in his will. A good sign, as it showed that Henry of York was willing to respect the wishes of his late Father. Henry would soon begin to govern with the Chamber, which advised Henry and the young King on matters of state. He also had several advisors of his own, including Thomas More and the Earl of Devon. Annoyingly for Henry, they'd soon begin trying to limit the number of grants he handed out.”

- Gregory Johnson, “The Regency of King Arthur I”​

“Henry VII would be buried at Westminster Abbey on February 4th. He would be laid to rest next to his Mother, Lady Margaret Beaufort and his son, Arthur, Prince of Wales. At his tomb there was extra space for his wife’s coffin, as he had wished to be buried with her. Elizabeth of York would not attend the funeral, as was tradition, but she would also not make an appearance at Court for 3 weeks, highlighting how devastated she was. She would wear mourning clothing up to 1515, when she finally left mourning. There is little doubt that it was her daughter and youngest child, Mary who comforted her.”

- Alex K. Chandler, "Henry VII: From an Exile to a King​

“The King and his brother quickly took residence at the Grand Palace of Richmond. Bernard André and I continued to educate them and would see to it they were the finest Royals in all of Christendom, as per their Uncle and Grandfather’s request.”

- Polydore Vergil, “The History of the reign of King Arthur the first”​

“With Prince Henry now Lord Protector, Princess Mary and Thomas Howard now decided it was no or never. If they were to ever become husband and wife, it had to happen under Henry. This was because Henry was fond of Mary, who was his favourite sister. He was also quite generous as Lord Protector, removing fines imposed on nobles by his Father, and approving all sorts of marriages and deals. Quickly, Thomas and Mary put their plan into action.

First, they were to get the backing of Thomas’s family, who were growing more prominent every day. With their backing they could increase the chances of Henry agreeing. Next, they were to request the backing William Warham, a key advisor to Henry and the Archbishop of Canterbury, the leading Archbishop in England. They hoped this would get them the backing of Henry. They would then request the betrothal to Prince Christian be broken, which would leave the two free to marry. They would also need to get a Papal Dispensation to marry, as they were 1st cousins and the Church did frown upon cousin marriages unless they had a Papal Dispensation.

They would quickly prepare to put their plan into action. The plan was only hastened when news arrived that Prince Christian’s Father had fallen ill. The plan would prove to be one of the most audacious in English history.”

- Tatianna Howard, “The Story of Mary Rose Tudor”​

For Polydore Vergil's book I was thinking of using this to have it written in Middle English, the form of English he would've spoken. Let me know if you want me to use it.
Nice(ish) that Mary and Thomas are plotting, hopefully they don't get into too much trouble and Henry is somewhat lenient.
I mean, such a marriage wouldn't be as scandalous as Mary's second marriage in OTL, since Thomas is related to the Royal Family and is a member of one of the most prestigious houses in England.
Section 12: Wacky Court Politicking
“Catherine of Aragon was quick to ask the Regency Council for permission to visit her sons twice a week. The Regency Council denied her, her request, and left it at the regular twice a month schedule. Catherine was enraged by this; she was the Queen Mother and the Ambassador to England; those positions alone should be enough for her to see her sons more often. She would quickly begin to befriend many of Henry’s advisors in a bid to get her request accepted.”

- Liam Christy, “Catalina de Aragon”​

“Early on during his Regency, King Arthur was taken to Court, where he would attend Council meetings and Parliament. They would discuss taxes, trade, diplomacy, etc. They also planned to begin negotiating the handover of Edmund de la Pole, a Yorkist claimant, to England. Edmund was currently taking refuge in Burgundy as a guest of Duke Charles. The matter would quickly be sent to the Ambassador to Burgundy, Thomas Boleyn, and long negotiations over the handover began.”

- Jeanne Laurence, “The Children of Camelot”​

“Arthur Plantagenet was perhaps the most unusual person in King Arthur’s court. Arthur was the bastard son of King Edward IV and a mistress of his, making him the half-uncle to Henry of York and the half-Granduncle of King Arthur. He had served as a member of his half-sister Queen Elizabeth of York’s household and had recently been made a member of Henry’s bodyguard. The two soon became friends, and as such Henry decided to try and promote Arthur, who was title less. Firstly, Henry, with the young King and Council’s permission knighted, Arthur Plantagenet. Secondly, Henry began searching for a bride for Sir Arthur Plantagenet

There was an heiress readily available for Arthur to marry, Elizabeth Grey, Baroness Lisle. Henry would have married her to Charles Brandon if not for the fact Brandon’s Wife Anne Browne was still alive. As such he would give Elizabeth Grey and her lands to his other favourite, Arthur Plantagenet. Though Elizabeth was 30 years his junior, Henry figured the match would be a good way to increase Arthur Plantagenet’s ranking. As such he would betroth Arthur Plantagenet to Elizabeth Grey. He also attempted to grant him the title Viscount Lisle, though the council refused, despite the King's agreement. However, Henry would find a work around as he granted the title through an act that did not require the Council’s approval. As such, Arthur Plantagenet became Viscount Lisle, and hence forth shall be referred to as such to avoid confusion with King Arthur.”

- Grace Lisle, “The Last Plantagenet: Arthur, Viscount Lisle”​

“In May of 1513, Anne Hastings fell pregnant yet again. Unlike her first pregnancy, her Husband did begin to suspect something. Of course, he did not do this openly, but we know from a recently discovered Journal that belonged to him that he was suspected Anne of something. He had not bedded his Wife since she gave birth, for he feared that it may cause her harm. He must have also noticed how much time Anne and Henry spent together. Regardless a few months later in 1514, Anne would give birth to a girl, who was named Mary after George’s Mother.”

- Tyler Scott, “Henry and the Annes”​

“Not long after the Regency began Thomas Howard and Princess Mary put their plan into action. They would inform the Howards of their desire to marry and were quickly given their support. They then began to try and convince John Fisher to back them. After much pleading, they succeeded and Fisher agreed to back them, their plans were slowly coming to fruition.”

- Tatianna Howard, “The Story of Mary Rose Tudor”​
it would definitely be nice for catherine to be able to see her sons more but at least she has her daughter to mold into the perfect christian renaissance queen and princess. and i have a feeling that henry of york isn't going to like what his sister and howard have planned...
it would definitely be nice for catherine to be able to see her sons more but at least she has her daughter to mold into the perfect christian renaissance queen and princess. and i have a feeling that henry of york isn't going to like what his sister and howard have planned...
Indeed, Catherine is going to make sure Elizabeth becomes the most educated Princess in Europe! As for Henry of York, he’ll definitely be in for a surprise when Mary and Thomas’s plan comes to fruition.
Interesting (but not surprising) to see some friction between Catherine and Henry.. Oh boy, Mary's little plan well soon come to fruition, excited to see how it goes..
Interesting (but not surprising) to see some friction between Catherine and Henry.. Oh boy, Mary's little plan well soon come to fruition, excited to see how it goes..
I mean, Catherine and Henry are pretty much destined to but heads of Henry is Regent for her kids. They’ll both have two different views on what to do.

As for Mary’s plan it is slowly coming together!
Is Catherine gonna stay in England forever? Seems like she could remarry to the Duke of Savoy/King of Portugal or become regent for Castile and help Charles.

Yes, yes, I know. I'm broken record.
Is Catherine gonna stay in England forever? Seems like she could remarry to the Duke of Savoy/King of Portugal or become regent for Castile and help Charles.

Yes, yes, I know. I'm broken record.
Most likely yes, she is the Spanish Ambassador to England, and will likely stay as such until after Ferdinand II dies, and by then Arthur will be of age and might just keep his Mother around, just so she can see her Grandchildren be born and grow up.
She's still young enough for more children.
True, and I have thought about having her remarry to an English noble, or a second son of a foreign ruler, but for all a potential suitor may know, she may not be able to have more children due to her giving birth to triplets at 17.
She's still young enough for more children.
Not if she stays in England. A Dowager Queen young enough to marry and have kids after the Kings death is exactly what happened when Henry V died, and Catherine Valois married Owen Tudor. If Katherine wants to stay in England, neither the Council, nor Henry of York, would allow her to remarry.

They won't want history repeating itself...
Great update! Tensions are starting to show at the court of England...also, Elizabeth Grey is 7? And Arthur, Viscount Lisle is 37...ahh, well, rather squicky but it wasn't uncommon...although Google is telling me that Elizabeth was only betrothed to Charles Brandon because she was his ward after her stepfather died...so how does that work? Does Arthur get the wardship? Because Elizabeth's guardians IOTL had a habit of marrying themselves or their male heirs to her...

Also, like @vandevere said, Katherine's not remarrying at all if she wants to continue raising and seeing her children on a regular basis, since if she goes abroad for remarriage she'll probably be like Eleanor of Austria, where she didn't see her daughter for 28 years after remarrying. She's definitely not becoming Catherine of Valois 2.0 if, again, she wants to see her children. Her parents may have wanted to bring her home for remarriage, but then again, as the King's Mother, she can still wield a lot of influence in England...