Robert Graham is presently identified as a son of John Graham. fourth Earl of Montrose, and his wife Margaret Ruthven, but evidence of relationship has not been included in his profile overview. Moreover, according to the Scots Peerage, the Earl and his wife did not have a son named Robert.
Can anyone provide evidence of relationship?
The Scots Peerage VI: 241
https://archive.org/details/scotspeeragefoun06pauluoft/page/241/mod...