Mary Queen of Scots 1542-87 married Henry Stuart (Ld. Darnley) 1545-67 who was son of Matthew Stuart, 4th Earl of Lennox.
Mary Queen of Scots had a 1/2 brother, Robert Stewart who married Janet Kennedy. Janet's sister, Helen Kennedy married William Adair of Kinhilt. This made William Adair brother-in-law to 1/2 brother of Mary Queen of Scots.
Mary Queen of Scots had son King James VI of Scotland who ascended the English throne 24 March 1603 as King James I (of England).
Therefore this may have made King James VI of Scotland (King James I of England) 1/2 nephew-in-law of William Adair of Kinhilt. (I am phrasing this in a simple way, perhaps someone can give the correct relationships).
"....(Kennedy's) half-sister Helen married William Adair of Kinhilt, a family who were favoured by the patronage of James VI." (This would have been much later than about 1547 when Wm & Helen were married).