Gilles II Aycelin de Montaigu or Montaigut, Montagu, was a French religious and diplomat who became Lord Chancellor of France, Cardinal from 1361 and bishop of Frascati from 1368. He was the chief negotiator for Jean II of France with the English, in the aftermath of the battle of Poitiers. Towards the end of his life he lived in Avignon on a livery from Cambrai. He died in there on 5 December 1378.
Born in the early years of the 14th century, Gilles Aycelin came from an Auvergnat family with several prominent members in his period. Brother of Pierre Aycelin de Montaigut, and nephew of Gilles I Aycelin de Montaigu, "the Elder", he was bishop of Lavaur (1357-1360) and then bishop of Thérouanne (1356–1361),bishop of Frascati (Tusculum) (1368-1378) and cardinal-priest with the title of SS. Silvestro e Martino (1361-1368).
He attended in 1356 the disastrous Battle of Poitiers and followed King John II of France, "the Good", in England with the title of chancellor. In May 1358 he was sent to London by King John II to lead the council of his son, John, Duke of Berry, "the Magnificent", Count of Poitiers. On 24 June 1360 he went Carcassonne to the marriage of Count of Poitiers with Jeanne, daughter of John I, Count of Armagnac, dead in 1388. John II, "the Good", obtained for him the cardinalate from Pope Innocent VI in 1361.