1670: June
On June 1, eight-year-old King Carlos II of Spain has an epileptic fit; his mother, Mariana of Austria, continues as Queen Regent. It's not an unusual state of affairs for the sickly last son of the Spanish Habsburgs, until he doesn't wake up.
On the same day, King Charles II of England and King Louis XIV of France sign the Treaty of Dover in secret. George Villiers, 2nd Duke of Buckingham and a member of the English king's private "Cabal" of political allies, is dispatched to France to draw up a public treaty.
The Spanish king's continued absence is eventually noticed and demands begin for news about his health. Mariana denies rumors that her son is dead. Don Juan José, Viceroy of Aragon and illegitimate half-brother to the king, leads the main opposition. Eventually her pet confessor is captured and confesses: the boy died three days after his collapse.
A coup ousts the Queen Regent and the various Cortes meet to decide on the succession. Louis XIV positions his second son Philippe Charles, Duke of Anjou (and not yet two), as the next heir to the Spanish throne. Johan de Witt of the Netherlands objects and demands an international conference to decide the succession. Buckingham remains in France and continues works toward a British/French coalition against the Netherlands and now Spain.
On June 27, Stadtholder William of Orange arrives in Spain and begins discussions with Juan José over international involvement in the Spanish question. He believes England, in the form of his uncle Charles II, could pressure France to negotiate.
1670: July
Public opinion in England is against a French royal taking the Spanish throne. Lord Anthony Ashley Cooper (
3rd Earl of Shaftesbury and another Cabal member) speaks against the potential "horrors of a dictatorial empire" should the two crowns fuse.
In France, the exiled Edward Hyde (Earl of Clarendon, former Prime Minister, and father-in-law to the English king's brother James) discovers evidence of the Treaty of Dover, including a provision that Charles II would convert and bring England back under Catholicism. He is horrified and sends word back to friends in Parliament. By sheer bad luck the letter is left unattended, found, and printed as a pamphlet. A public scandal erupts; protests by nonconformists converge in London, demanding the Conventicles Act of 1664 be revoked (with support from Scottish presbyrs). The Cabal Ministry is divided on the issues; with Buckingham out of town, Ashley urges the King to deny the charges.
I started this timeline three years ago as a thought experiment and the vague goal to bring England and the Netherlands closer together. I originally posted it on Althistoria last year; there may be some edits/changes to the version posted here, especially in the later years that need to be fleshed out more. Any and all feedback/critique is welcome.
Edited 12/4/2017: I forgot that The Lord Ashley ain't an Earl yet in 1670.