 In 1297 , Joan secretly married Ralph de Monthermer , a knight in the late earl 's household . This enraged Edward I , who had other marriage plans for Joan . The king imprisoned Monthermer , but later relented , and sanctioned the marriage . Because of the previous settlement , Joan was still titled countess , and her new husband became Earl of Gloucester and Hertford . This , however , only lasted for the life of Joan , who died in 1307 . Only a few months later , Gilbert was granted his inheritance , and by March 1308 made Earl of Gloucester and Hertford , at the young age of sixteen . This grant was made by Edward II , who succeeded his father Edward I in July 1307 . It was previously believed that Edward II and Gilbert were brought up together , but this is based on a confusion with another person of the same name . This other Gilbert de Clare , who was closer to the king in age , was in fact the earl 's cousin , the son of Thomas de Clare , Lord of Thomond . 
