No exact birth dates are known for any of the sisters, all were born within the aforementioned timeframe but Constance was most probably the eldest because she inherited Martha's estates when she died.
[3] A marriage contract was signed at Seville, with Constance's sister Guilemette being betrothed to Manuel's son Alfonso.
[4] A third marriage contract was drawn up in 1268, for Constance to marry Henry of Almain,[5] a grandson of King John of England.
She had made Simon de Montfort, 6th Earl of Leicester, governor of Bigorre and upon her death, he had refused to hand over control to Constance's aunt Alice.
Her father, Gaston then assisted his daughter by attacking Bigorre, which was once again occupied by Simon de Montfort.
The overlord, Edward I of England, did not like the thought of a union between Béarn and Bigorre so had John Grailly placed there as general, forcing Gaston to pull back.
[9] Bigorre then remained under French control until it was claimed in 1425 by John I, Count of Foix, a descendant of Constance's sister, Margaret.