The family descended from the Bruces of
Clackmannan, whose ancestor was
Thomas de Bruys. According to Sir
James Balfour Paul, there is no evidence that this branch of the family was descended from
Robert the Bruce (King Robert I), despite claims that Thomas was an illegitimate son of the king. However, King Robert's son
David II made a grant of land in 1359 to
Robert Bruce referring to him as
dilecto consanguineo suo (our beloved cousin). It was generally accepted that Clackmannan branch descended from
John de Brus who was a younger son of
Robert de Brus, 5th Lord of Annandale. The first earl was succeeded by his son, Robert, who also was created
Earl of Ailesbury in the Peerage of England. The two Earldoms continued united until the death of the fourth Earl of Elgin, when the Ailesbury and Baron Bruce (of Whorlton) titles became extinct, and the Elgin title passed to the
Earl of Kincardine; the
Lordship of Kinloss became dormant. Thereafter, the Earldoms of Elgin and Kincardine have remained united. ==Feudal Barons of Clackmannan==