According to The Brus they were married, but The Scots Peerage points out that this is unlikely because he did not immediately inherit his father's lands and titles; Freedom's Sword also says he was illegitimate.
It is stated by The Brus that they got married, however The Scots Peerage argues that this is unlikely as he didn't immediately take over his father's properties and titles; Freedom's Sword also claims that he was the offspring of an illicit union.