On 9 March 1325, Queen Isabella departed from England for France to negotiate between her husband Edward II and her brother Charles IV, then at war with each other in the little-known War of Saint-Sardos, which I really must write a post about sometime. Isabella sailed from Dover with a large retinue and of course the full knowledge and permission of Edward II, and also with the blessing of Pope John XXII, who called her an "angel of peace" and had urged her to go to France to bring about an end to the conflict between her husband and her brother. The later chronicler Jean Froissart, born in about 1337, invented a tale where Isabella and her son fled from England in secret from Winchelsea after pretending to go to Canterbury on pilgrimage, a very silly and inaccurate story followed rather too slavishly by some other writers. There's a theory that Charles IV was conspiring against Edward II, possibly with Roger Mortimer (who escaped from the Tower of London on 1 August 1323 and made his way to the continent), and deliberately engineered Isabella's 'escape' from England with the knowledge that she was going to act against her husband in cahoots with Roger. This would need another blog post to sort out, so let me just say at this point that I think this story is extremely unlikely and based on nothing more than hindsight and imposing an order and pre-conceived pattern which never existed on the chaos at the end of Edward II's reign.
Isabella's itinerary in France still exists: she passed through Boulogne, where she and Edward had married seventeen years previously; Montreuil, part of Edward's inheritance from his mother which he gave to her in 1308; Crécy, where her and Edward's son Edward III would win a famous victory against the French twenty-one years later; Beauvais and Pontoise, where on 20 March she dined with her sister-in-law and first cousin Jeanne d'Evreux, queen of France and Charles IV's third wife, and other members of her family. On 21 March, she met her brother Charles IV at Poissy, and began the difficult negotiations which resulted in a peace treaty between England and France on 30 May.
Isabella sent Edward II a letter on 31 March 1325, admitting she was finding her brother very harsh to deal with (lui trovoi deur). She was, presumably, very angry with Edward at this time: he had confiscated her lands six months previously and, because of the war with France, removed her French servants from her household (he didn't remove her children from her, however; this is a modern myth with no foundation). Or at the very least, she was angry with Hugh Despenser the Younger for persuading Edward to do these things, and, one imagines, also deeply annoyed with Edward for allowing Hugh to do so and to treat her so disrespectfully. There is no sign in her letter of any anger, however, which is long and affectionate and addresses Edward five times as "my very sweet heart," mon tresdoutz coer.
Edward and Isabella never met again after 9 March 1325, or at least, there's no evidence that they did. I've written a post, and see also this one, about their complex and fascinating relationship. Sometime in the late autumn or early winter of 1325, Isabella made the momentous decision to stay in France and not return to Edward, and made a long and dramatic speech to the French court (recorded by the Vita Edwardi Secundi) declaring that she would wear widow's clothes until she was "avenged of this Pharisee," i.e. Hugh Despenser the Younger, who had destroyed her marriage. She stated on several later occasions that she felt herself unable to return to her husband because of the physical danger to herself from Hugh, whom she utterly loathed and on whom she avenged herself by having him grotesquely executed on 24 November 1326. At some point before 8 February 1326, when their names were linked together in a proclamation by Edward II complaining that his wife was consorting with "the king's notorious enemy and rebel," she began a relationship with Roger Mortimer, though we really don't know the true nature of their relationship, whatever may be claimed nowadays.
As late as 5 February 1326, after her refusal to return to England and her husband, Isabella referred to Edward II in a letter to Walter Reynolds, archbishop of Canterbury, as "our very dear and very sweet lord and friend," nostre treschier et tresdouche seignur et amy. This is a very unconventional way of talking about your husband - 'our very dear lord' would be conventional - and hints at some deep feeling she held for him. Another intriguing aspect of an intriguing relationship; take no notice whatsoever of modern writers who claim that the pair loathed and despised each other. They didn't. There is also absolutely no reason to suppose, as one modern writer has claimed, that Isabella felt "profound revulsion" for Edward in 1325/26 or at any point ever. Isabella also stated in her letter "...we desire, above all else, after God and the salvation of our soul, to be in the company of our said lord [Edward] and to live and die there" and that no-one must think that she had left her husband "without very great and justifiable cause," i.e. feeling threatened by Hugh Despenser, who, as she pointed out, had full control of the king and his realm. This may, of course, be the queen's attempt to keep up appearances, but it may well be true. We don't know when she decided that her husband should be removed from power, and it may even have been well after her invasion force landed in England on 24 September 1326. I'll discuss this point in a future post, and will just say here that the assumption that Isabella had been planning Edward's downfall for years is just that, an assumption.
Sources: Isabella's letter of March 1325 is printed in full (in the original French) in Pierre Chaplais, ed., The War of Saint-Sardos (1323-1325): Gascon Correspondence and Diplomatic Documents, Camden third series, lxxxvii (London, 1954), pp. 199-200, and the letter of February 1326 is cited in Seymour Phillips' Edward II (London and New Haven, 2010), p. 491.