Uriel was a sl*t. Martin's not even his first illegitimate son.
It's not even uncommon for Kings in the Real World to have lots of illegitimate offspring -they can literally have anyone they want, and I'm sure Uriel did.
Edit: damn word censor, I should be able to say [censored].
There is another.
Sorry, couldn't resist
Seriously, though, where did you acquire this information? Not to be skeptical, but if this is true, he was probably dead before the events of Oblivion.