Travelling to France on a diplomatic mission, Isabella may have begun an affair with Roger Mortimer, and the two may possibly have agreed at this point to depose Edward and oust the Despenser family.

Isabella and Mortimer's regime began to crumble, partly because of her lavish spending, but also because the Queen successfully, but unpopularly, resolved long-running problems such as the war with Scotland.

She lived out her remaining years as a wealthy courtier and grew close again to her family especially her daughter Joan, Queen of Scots and her grandson Edward, Prince of Wales.

[9] Philip built up centralised royal power in France, engaging in a sequence of conflicts to expand or consolidate French authority across the region, but remained chronically short of money throughout his reign.

[23] When Isabella first arrived in England following her marriage, her husband was already involved with Piers Gaveston, an "arrogant, ostentatious" soldier, with a "reckless and headstrong" personality that appealed to Edward.

[14] Baronial opposition to Gaveston, championed by Thomas of Lancaster, increased; and Philip IV began to covertly fund this grouping, using Isabella and her household as intermediaries.

Thomas of Lancaster reacted to the defeats in Scotland by taking increased power in England and turning against Isabella, cutting off funds and harassing her household.

[51] At this point, Isabella undertook a pilgrimage to Canterbury, during which she left the traditional route to stop at Leeds Castle in Kent, a fortification held by Bartholomew de Badlesmere, steward of the King's household who had by 1321 joined the ranks of Edward's opponents.

[53] Whilst Edward mobilised his own faction and placed Leeds Castle under siege, Isabella was given the Great Seal and assumed control of the royal Chancery from the Tower of London.

Criminal gangs were occupying most of the country and there had been an assassination plot against Edward and Hugh Despenser in 1324, with the famous magician John of Nottingham being hired to kill the pair using necromancy.

[citation needed] Having promised to return to England by the summer, Isabella reached Paris in March 1325 and rapidly agreed to a truce in Gascony, under which Prince Edward, then thirteen years old, would come to France to give homage on his father's behalf.

[84] She then used this money, plus an earlier loan from Charles,[85] to raise a mercenary army, scouring Brabant for men, which were added to a small force of Hainaut troops.

[91] The local levies mobilised to stop them immediately changed sides, and by the following day Isabella was in Bury St Edmunds and shortly afterwards had swept inland to Cambridge.

[89] Isabella struck west again, reaching Oxford on 2 October where she was "greeted as a saviour" – Adam Orleton, the Bishop of Hereford, emerged from hiding to give a lecture to the university on the evils of the Despensers.

[99] By now desperate and increasingly deserted by their court, Edward and Hugh Despenser the Younger attempted to sail to Lundy, a small island in the Bristol Channel, but the weather was against them and after several days they were forced to land back in Wales.

[100] With Bristol secure, Isabella moved her base of operations up to the border town of Hereford, from where she ordered Henry of Lancaster to locate and arrest her husband.

Hugh Despenser the Elder had been captured at Bristol, and despite some attempts by Isabella to protect him, was promptly executed by his Lancastrian enemies – his body was hacked to pieces and fed to the local dogs.

After the funeral, there were rumours for many years that Edward had survived and was really alive somewhere in Europe, some of which were captured in the famous Fieschi Letter written in the 1340s, although no concrete evidence ever emerged to support the allegations.

The conventional 20th-century view has been that Edward did die at Berkeley Castle, either murdered on Isabella's orders or of ill-health brought on by his captivity, and that subsequent accounts of his survival were simply rumours, similar to those that surrounded Joan of Arc and other near contemporaries after their deaths.

Unlike Mortimer, Isabella survived the transition of power, remaining a wealthy and influential member of the English court, albeit never returning directly to active politics.

Isabella reopened negotiations in Paris, resulting in a peace treaty under which the bulk of Gascony, minus the Agenais, would be returned to England in exchange for a 50,000-mark penalty.

[129] The French nobility were unimpressed and, since Isabella lacked the funds to begin any military campaign, she began to court the opinion of France's neighbours, including proposing the marriage of her son John to the Castilian royal family.

[136] The execution itself was a fiasco after the executioner refused to attend and Edmund of Kent had to be killed by a local dung-collector, who had been himself sentenced to death and was pardoned as a bribe to undertake the beheading.

[138] Edward quietly assembled a body of support from the Church and selected nobles,[139] whilst Isabella and Mortimer moved into Nottingham Castle for safety, surrounding themselves with loyal troops.

[147] Agnes Strickland, a Victorian historian, argued that Isabella suffered from occasional fits of madness during this period but modern interpretations suggest, at worst, a nervous breakdown following the death of Mortimer.

[153] She remained, however, a gregarious member of the court, receiving constant visitors; amongst them appear to have been her friend Marie de St Pol, Countess of Pembroke, and her cousin Henry of Grosmont, Duke of Lancaster.

[151] She remained interested in Arthurian legends and jewellery; in 1358 she appeared at the St George's Day celebrations at Windsor wearing a dress made of silk, silver, 300 rubies, 1800 pearls and a circlet of gold.

[155] Isabella took the nun's habit of the Poor Clares before she died on 22 August 1358 at Hertford Castle, and her body was returned to London for burial at the Franciscan church at Newgate, in a service overseen by Archbishop Simon Islip.

Isabella left the bulk of her property, including Castle Rising, to her favourite grandson, the Black Prince, with some personal effects being granted to her daughter Joan.

In contrast to the negative depictions, Mel Gibson's film Braveheart (1995) portrays Isabella (played by the French actress Sophie Marceau) more sympathetically.