On 20 October 1312, Edward II granted his queen Isabella of France permission to make her will. Isabella was then about eight months pregnant with their eldest child the future Edward III, who was born on 13 November. As a married woman, Isabella needed her husband's permission to make her will, and it was a common thing for pregnant women to do in an age when pregnancy and childbirth were so risky. Professor Seymour Phillips suggests in his Edward II (2010, p. 204) that Isabella was having a difficult pregnancy and feared death in childbirth, and that Edward was thus probably concerned with his wife's spiritual welfare. Phillips also points out, however, that a copy of Edward's permission and his granting her all her movable goods (see below) survives in the Archives Nationales in Paris, which suggests that the French envoys then in England to negotiate between the king and Piers Gaveston's killers had suggested that Isabella make a will to ensure that the terms of her dower continued in case of her death.
Unfortunately Isabella's will itself has not survived, which is a real shame. Edward's permission and granting to her of her goods and lands, however, appears in Rhymer's Foedera, Conventiones, Litterae, vol 2, part 1, p. 184, in the original French, and is briefly calendared on the Patent Roll (1307-1313, p. 508: "The king grants authority to queen Isabella to dispose of her goods and jewels by will.") Here's my translation of the long Foedera version:
Edward, [by the grace of God king of England] etc, to all those who see and hear these present letters, greetings in our Lord.
Be it known to all that because we know well that nothing is as certain as death, nor less certain than the hour at which it may come, we give and grant permission to our very dear consort Isabella, by the same grace queen of England, lady of Ireland and duchess of Aquitaine, that she may make and draw up her testament or her last will regarding the temporal goods which God has given to us and to her; at the same time and by this testament or last will, accomplished and carried out by the hand of her executors, we give and grant to her now all the movables which are and will be hers; all her vessels of gold and silver; all her jewels in whatever place they are or will be found.
Further, we give and grant her all the county of Ponthieu, and the land of Montreuil, and all the other lands which she holds and will hold of our gift, whether in the realm of England or in France, or elsewhere, that it may be levied or exploited by the executors or at their command, for three years continually [I've chopped this bit talking about lands and rents, as it's really boring].
And further, by our leave and special permission, we wish that, wherever it may best please her, she may have the said executors purchase 1000 pounds sterling of land which by our present letters we will alienate for her holding, to make and establish a hospital where poor people will be rescued, lodged and laid to bed, for the safeguard of our [Edward and Isabella's] souls.
And because all the things stated above shall be valid and binding for always, without ever being opposed by us or by others, whoever they may be, we have had these open letters sealed with our great seal.
Given at Windsor on the twentieth day of the month of October, year of grace one thousand, three hundred and twelve, and the sixth of our reign.
Edward II was, to my knowledge, the only medieval king of England who died intestate. His father Edward I made his will when on crusade in the Holy Land on 18 June 1272, when his father Henry III was still alive, and oddly enough never updated it, despite living for another thirty-five years. He made it in Acre, to be precise, where his daughter Joan, countess of Gloucester, was born, probably around the same time. Edward II's father-in-law Philip IV of France made his main will in May 1311, and added a codicil to it on 28 November 1314, the day before he died (when he presumably knew that he was dying). Philip's main will does not mention Isabella, but in the codicil he left her two rings, one of which she had previously given him, and a cup, which she had also given him. (Seymour Phillips, Edward II, p. 223.) Edward and Isabella's son Edward III made his will at Havering-atte-Bower on 7 October 1376, a few months before he died and several months after the death of his eldest son Edward of Woodstock, prince of Wales.