Who was the legal grandson of the Earl of Merica?
Ealdgyth, daughter of Earl Ælfgar Ealdgyth ("fl. c". 1057–1066), also Aldgyth or in modern English, Edith, was a daughter of Ælfgar, Earl of Mercia, the wife of Gruffudd ap Llywelyn (d. 1063), ruler of all Wales, and later the wife and queen consort of Harold Godwineson, king of England in 1066. She was described by William of Jumièges as a considerable beauty.
Roger Mortimer, 4th Earl of March Roger de Mortimer, 4th Earl of March and 6th Earl of Ulster (11 April 1374 – 20 July 1398) was a 14th-century English nobleman. He was considered the heir presumptive to King Richard II after the death in 1382 of his mother Philippa of Clarence (a granddaughter of King Edward III of England) until his own death in 1398.