William Anderson’s book, “The Scottish Nation” (published in 1877), provides some compelling evidence for linking Blackadder to our Douglas family.

“Andrew Blackadder, the proprietor of the estate, married a daughter of the house of Johnston of Johnston, ancestor of the earls of Annandale, and had two sons, Robert and Patrick. Robert, the elder son, espoused Alison Douglas, fourth daughter of George, Master of Angus, and sister of Archibald, earl of Angus. He followed the standard of the Douglases at Flodden in 1513, and was slain with his father-in-law and two hundred gentlemen of the name of Douglas, on that disastrous field, leaving a widow and two daughters, Beatrix and Margaret, who, at the time, were mere children [Redpath’s Border History.]” [Anderson.1:309]

Sources:
Anderson, William. The Scottish Nation, Or, the Surnames, Families, Literature, Honours, &

Blackadder is a branch of Clan Home/Hume