|Katherine and Owen|
(credit to Luna Akaisha on DeviantArt)
Sure, there's no document that's come down to us screaming, "Katherine married Owen at such-and-such time and such-and-such place!! Believe me!!" But there's good reason for that. Owen was a relative common Welshman. Lately with the Glyndwr rebellion and all, the Welsh were mostly looked down upon in English society. And Katherine being the queen knew all the kinds of trouble she would get into for marrying a Welsh commoner. Thus, the two's wedding took place in secret.
Some skeptics might still be saying, "wait! That doesn't prove a thing!" Well then, what do you say to this?
While living their secret lives, Katherine and Owen stayed at the palaces of the their friends, the Bishops of Ely and London. Would ordained Bishops allow an unmarried couple to live together within their household? I don't think so! Both are known to be staunchly pious and wouldn't want two people committing sin in their own palace. And why! Even Richard III, who had every reason in the world to spew hate towards Henry Tudor (Katherine and Owen's descendant) never once even hinted at it. Instead he called Henry the descendant of Katherine of Valois and Owen Tudor, just like that. If the two had not been married don't think Richard would've brought that up when he famously talked about Henry's "bastard blood on both his father and mother's sides". From his mother's side? That's pretty obvious, the Beaufort line. From his father's side? This is more surprising! Richard made the astonishing claim that it was Owen who was illegitimate!
(Don't worry though, that last one's not true)
If one examines the many sources discussing and or mentioned Owen and Katherine's union, all agree that the two were in fact married.