This sounds like a reference to a piece of text your son was meant to read and so we're unlikely to come up with the answer.
An educated guess would be this portrait of Catherine of Aragon.
http://englishhistory.net/tudor/monarchs/arago n.html
He was married to her before he died and Henry ended up marrying her, Henry marriage required dispensation due to the biblical injunction against "marrying your brother's wife" which then was one of the complications preveenting him getting a divorce which was a driving force of the English reformation.
Arthur's marriage to Catherine is the only really imoprtant fact about him so I guess it'll be a reference to that.