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.
Earl of Ruglen Earl of Ruglen was a title in the Peerage of Scotland. Along with the subsidiary titles Viscount of Riccartoun and Lord Hillhouse, it was created on the 14th of April, 1697, for Lord John Douglas-Hamilton, fourth (third surviving) son of William Douglas-Hamilton, Duke of Hamilton, 1st Earl of Selkirk, and his wife Anne Hamilton, 3rd Duchess of Hamilton. The 1st Earl of Ruglen succeeded as 3rd Earl of Selkirk on the death of his elder brother in 1739. The Earl's only son William, Lord Daer, died in 1742, so on the death of the Earl of Selkirk and Ruglen in 1744, the Earldom of Selkirk passed to his great-nephew, while the Earldom of Ruglen passed to his daughter, Anne, who had married William Douglas, 2nd Earl of March. On her death in 1748, the Earldom of Ruglen passed to her only child William, 3rd Earl of March. He succeeded his first cousin once removed Charles Douglas as 5th Marquess and 4th Duke of Queensberry in 1778.