The 8th Earl of Douglas had been murdered in 1452 at Stirling Castle, by his monarch James II while under assurances of safe-conduct.

Other notable magnates had assisted King James in the act.

The whole of Douglasdale rises in rebellion under the late Earl's younger brothers, James, the new 9th Earl of Douglas, his twin Archibald Douglas, Earl of Moray, and the younger Hugh Douglas, Earl of Ormonde, and John Douglas, Lord of Balvenie.

During this time of intermittent internecine strife in Scotland, it would have been expected that Angus would have thrown his lot in with his Douglas cousins.

If this had been the case it could have spelled disaster for the House of Stewart.

Contemporary opinion would not have been surprised if he had, but as alluded above the ties of kinship were closer between Angus and King James were close, being first cousins within one degree.

A magnate as powerful as Angus could not abstain from declaring himself either way.

So, when the rebellion began in earnest in early 1455, and the King takes to the field against the Douglas brothers, Angus comes out in full support of his Monarch, and is given high command within the Royal army.

It has been suggested that Angus accompanied the King at the siege of Abercorn.

Following the defection of James Hamilton, 1st Lord Hamilton, Douglas' chief lieutenant to the King's side, the Earl of Douglas flees to England in an attempt to gain support from Henry VI of England.

Douglas' brothers stay in Scotland to continue the struggle.

The brothers appear in force in Annandale and King James sends Angus to deal with them.

Angus musters the Border Clans and encountes the rebels on the 18th of May near Langholm.

The ensuing Battle of Arkinholm is a rout for the Douglas brothers, Moray is killed and Ormonde captured (to be executed soon after) and only Balvenie escapes to England.

in the summer the Black Douglases are attainted and their estates declared forfeit.

Angus appends his seal to the charter in token of approval.