When Eleanor was thirteen years old, her father Simon de Montfort, and brother Lord Henry were killed at the Battle of Evesham (4 August 1265).

After Earl Simon's death, his family was forced to flee the Kingdom of England: Countess Eleanor took her daughter to the safety of the Dominican nunnery at Montargis, France, a Montfort foundation.

The two ships carrying Eleanor, her brother Amaury and their entourage, sailing off the south coast of England, were captured by sailors from the port of Bristol, just off the Isles of Scilly.

[2] 'Thomas Larchdeacon', 'Thomas the Archdeacon', who masterminded the capture on behalf of her first cousin Edward I of England was paid £20 in May 1276 by the king's orders, through the sheriff of Cornwall.

Before the wedding mass was celebrated, Edward insisted that Llywelyn should put his seal to an adjustment to the agreement that they had previously made.

[9] Eleanor had a daughter, Gwenllian of Wales, whom she died giving birth to on 19 June 1282[10] at the royal palace in Abergwyngregyn, on the north coast of Gwynedd.