Sir John Graham, 9th Earl of Menteith in right of his wife (see Montrose, D). [Burke's Peerage]
The citation in Burke's Peerage for this John refers to the lineage of the Dukes of Montrose that contains a John who I have as father of this John, and several internet sources indicate that this John is the son of a John, so I believe this relationship is correct. However there is nothing in Burke's which absolutely nails the relationship down. Many have John a descendant of Patrick, which I have with an intervening John who was living 1317 according to Burke's. However many have John the son of Patrick who married Annabella, while, according to Burke, Annabella married Patrick's father David (They had a son John who died at the Battle of Falkirk in 1289). Some have John the son of John of Abercorn which would have been a different line departing from this line up at the beginning with Peter son of William.
17 Oct 1346 - Captured at Battle of Neville's Cross--and subsequently executed by the English.