A while back there was a discussion about the identity of this Andrew Stewart. The discussion must have been private because I don't find it here in the public discussions. (That's the problem with private discussions -- they don't reach a full audience and their content is easily lost.)
At the time I made a note to check the old manuscript histories. It has taken me quite a while to do that.
This Andrew married Maud Grant of Stratherrick, heir of Stratherrick, the heiress of the Grant chiefs.
The Monymusk Text (circa 1710) says "Marjory, or Mald, daughter and representative of Grants, was left by Patrick heretrix of Freuchy, Strathernick, and Glenchernich, to the tuition of his nearest friends, with this Mandate, [p16] that whoever should be joined in marriage to her should of necessity be of the name of Grant." He is described as "Andrew Stuart, Sheriff of Boot, a young man of deserved renown, pursuing his fortune".It tells the story of the lovers then says, "Att length Andrew Stuart and the heiress of Grant are orderly and solemnly married about 1210, and lived quietly and comfortably together for many years".
http://www.clangrant.org/index.aspx?pid=14
The Cromdale Text (1729) calls her Mald, daughter of Sir John Grant of Fruichy and Stratharrick, and says, "he married Andrew Stuart Son to The Sheriff of Bute, who by Articles in The Marriage changed his Name, and was called Andrew Grant alias Stuart."
http://www.clangrant.org/index.aspx?pid=16
The Tullochgorm Text (circa 1770) repeats the Monymusk Text.
http://www.clangrant.org/index.aspx?pid=49
The Shaw Text (1775) mentions miscellaneous early Grants then says, "I cannot, indeed, instruct that these five gentlemen were the successive representatives of the family, although I think it highly probable. But the following descents, from father to son, admit of no question, viz: (6) Maude or Matildis, heiress, married Andrew Steuart, son of Sir John Steuart, Sheriff of Bute, who was son of King Robert II".
http://www.clangrant.org/index.aspx?pid=17
Finally, the Baronage Text (1798) skips over the idea of an heiress, making the entire line father to son. This was the "canonical" version until modern DNA testing showed the Grant chiefs have the Stewart yDNA signature while other branches share a different yDNA signature. This fact makes it likely there was a break in the male line of the chiefs at some point and led to resurrecting the old histories.
http://www.clangrant.org/index.aspx?pid=18
The dates for heiress Mald and her husband are a bit scattered. If I remember correctly, that's why the previous discussion was struggling with his identity. The Clan Grant Society calls him Andrew (Stewart) Grant, 5th Lord of Stratherrick and says he was chief (about) 1320-1335. By implication, Mald would have been daughter of Sir John Grant, 4th Lord, who was chief (about) 1295-1320.
http://www.clangrant.org/index.aspx?pid=19
http://www.clangrant.org/index.aspx?pid=18
DNA seems to confirm a break in the male line about the 13th century , putting him in the timeline of the Andrew Stuart ..son on the 5th Stewart and Egidia "Giles" Stewart formerly Burgh aka de Burgh.
There might have been the split in the DNA here.
And or a NPE
But this mystery is close to being solved.
More ppl tested the better.