He was the son of Alexander Stewart, Duke of Albany, and his first wife Catherine Sinclair, daughter of William Sinclair, Earl of Orkney and Earl of Caithness.
[1][2] The marriage of his parents was dissolved in 1478 and his father remarried, but it was not until 1516 that an act of parliament made the marriage unlawful and ensured that Alexander Jr. would be regarded as legally illegitimate and unable to inherit his father's title.
[2] His high birth, however, enabled a successful career in the church.
[1] Between 1516 and 1518 he held a right to the commend of Whithorn Priory, a right he gave up to the papally-backed Silvio Passarini.
He was given crown nomination to the bishopric of Moray and then papal provision on 13 September 1529,[1] after the failure of the candidature of Alexander Douglas I.