McGehee Descenants, by Ethel Clyde Woodall Grider says that Patrick MacGregor supported the Royal cause 1644-45 and he served under Montrose. His wife was Marion MacDonald
This may have been why he was outlawed, as is ascertained in Marks-Barnett families and their kin., by Marion Dewoody Pettigrew 1939.
Alexander McDonald of New Inverness, Georgia: and his descendants - Page 23
by Daniel Huntley Redfearn - Reference - 1954 says, "Patrick MacGregor, Chieftain of that ilk, who led his clansmen unde Montrose in 1645, and was outlawed with his sons. His estates were confiscated---
Gray, Powers, and Their Interelated Families: Descendants of Col. Thomas ... - Page 260
by Edwina Gray Powers Ames, Stanley Richard Ames - Reference - 1992 says that he led 1000 fighting men under Montrose.
Debrett's Barontetage of England, By John Debrett –1839 says, "Patrick MackGregor afterwards joined Montrose in support of the royal cause with above a thousand of his clan, Mr. Nisbet, in mentioning the
loyalists, says, 'The MacGregors also, a clan inferior to none in bravery anc activity, followed their chief, Patrick.'
Patrick was in particular esteem with Montrose, two of whose letters are carefully preserved, addressed to 'His special and trusty friend, the honorable Patrick, Laird of Macgregor:' that great man, in the strongest terms, expressed his hearty approbation of his unshaken loyalty, and assured him that 'His Majesty's affairs being once upon a permanent footing, the grievances of his Family and Clan should be effectually redressed.' But their chief hopes died with this great hero; though they werein consequence of their loyalty, restored to their name, by act of parliament, in the reign of Charles II. Patrick m. Marian, daughter of MacDonald, of Auchatrichatan, chief of the most powerful tribe of MacDonalds in Glenco, by whom he had 3 sons: 1. John; 2. James/William, a major in the army, who went to America, where he married and acquired a great estate. He was at last killed by a party of rebelIndians. But some of his posterity still flourish near New York; 3. Duncan, d. Unm. John the eldest son, was a steady loyalist: he m. Ann, daughter of MacGregor, of Ross.
The same account appears in The New Baronetage of England: Containing, as Well a Concise Genealogical ... - Page 876--1804
Many researchers believe that James MacGregor changed his name to William MackGehee.