The current flag of Picardy derives from the banner of William IV of England & Ireland while he was the Red Prince of Picardy [1] and heir to the thrones of both England and Ireland.
The Red Prince’s banner was based on that of his uncle Eustace, Duke of Cornwall, Duke of Normandy, Count of Flanders, the Black Prince [of Picardy]; said banner flown during his campaign in Brittany to claim the Ducal Crown by right of wife [2]. Eustace’s death made the underage William heir presumptive to England, being the only son of Eustace’s sister Emma and King William III of Ireland, and led to the union of the crowns since King Eustace I of England created his 3rd son William King of Ireland [3].
William’s banner may also be considered to be the first merging of the English Red Cross of St George with the Irish Gold Cross of St Patrick [4] as it was later in William IV’s reign that the various Dual Monarchy flags are first seen, though flag most common in Normandy-Flanders (or Picardy as it became known) was the quartered crosses.
Variants of the Red Prince Flag surfaced during the occupation by the Burgundian Empire until the AngloIrish-Danian Coalition restored Picardy to the Regency.
A centred version of the flag served as official flag of the region until its appropriation by the Zirconists as the flag of the Zirconist Protectorate of Picardy. Members of the Resistance used a Danian-style [5] Red Prince Flag; this became the Regional Flag after liberation and remained so when the Region voted to remain part of a newly federalised restored Regency – the United Realms – as the Lieutenant State of Picardy.
The flag’s asymmetry in contrast to the other Lieutenant States is a strong reminder of the region’s independent character.
[1] so called due to his flaming red hair
[2] Eleanor daughter of Duke William of Brittany
[3] Eustace’s 1st son Henry died shortly after being made co-Duke of Normandy; his 2nd became Stephen I of England; his 4th became Eustace I of the Latin Roman Empire
[4] often also bearing 4 crowns
[5] OTL Nordic as Sweden-Norway uses saltires TTL
EDIT: a brief view of William IV's descent
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