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.
In accordance with The Brus, they were wedded, but The Scots Peerage suggests that this is improbable because he did not promptly inherit his father's estates and dignities; Freedom's Sword also asserts that he was born out of wedlock.