The negotiations leading up to ‘The Treaty of Dover’ were confined to a very few people in France and fewer still in England. Although the ‘CABAL’ knew of the general proceedings, the actual terms may only have been known to the English signatories: Arundel (Henry Howard), Clifford (Lord High Treasurer 1672-3), Arlington (Secretary of State 1662-74), and Richard Bellings (Queen Catherine’s Secretary). Colbert de Croissy, who had arrived in England in July 1668 and negotiated the key Treaty terms, was the signatory for King Louis of France. Henriette was clearly in Charles’ confidence and worked behind the scenes with Louis to bring the treaty about, and was probably responsible for settling final details directly with Charles.
I note that Philibert de Gramont was in England in 1667 buying horses, returning to France in January 1668 with Hamilton and Durfort Duras (Tree 2). Colbert de Croissy arrived in July that year. Then I see that de Gramont returns to France in October 1669 with a letter for Henriette (I have not seen when he had arrived in England).
With some difficulty Henriette obtained her husband’s permission for her to visit to her brother in England (the first since her marriage) and on 24/26 May 1670, accompanied by 237 people including the Count and Countess of de Gramont and Anthony Hamilton, she set sail for Dover where King Charles, the Duke of York, the Duke of Monmouth, Colbert de Croissy and many others awaited her. There was much feasting and celebration over the next ten days, and quietly behind the scenes The Secret Treaty of Dover was signed on 1st June 1670.