Do you know how old are really Jauffre and Martin ? TESCS ages are not accurate - if Martin is 50 and Jauffre 60, then Jauffre cannnot have been Uriel's captain when Martin was a baby. Looking at Martin, I'd say he is about 40. Which can't be if he is the son of Uriel, as he was the prisonner of Jagar Tharn at that time. So Martin has to be either younger than 34 or older than 44.
I've always wondered about the ages. I put Martin at early 30s - In Jauffre's in-game dialogue, he says that when Uriel gave him Martin to take away, he was Captain of the Blades. Now, if Jauffre is 60, surely this could not have been more than 30 years ago. I find it hard to believe that he could have achieved the post of Captain in his 20s. It's too young. To cement this, I'm sure the in-game response to asking Jauffre about Baurus triggers a reply that he is the youngest member of the Blades for a long time. Have I just imagined this? And Baurus himself is not much shy of 30, so from then it's just simple maths.
Considering these conversations, unless Jauffre was either a record-breaking prodigy in the Blades, or is much older than we thought, Martin cannot possibly be more than 35.
There is no irrefutable proof, and it would even be a better story if Uriel lied about Martin. he Emperor was portrayed like such a fool sometimes that he deserves a clever scheme. Say that he knew the true nature of the Covenant and the succession, and decided to support a good man over his dilettante grandchildren.
I like this idea. It could even be that Martin
does have a miniscule amount of watered-down Septim blood (considering how many bastards must have been born over the years), just not Uriel's. And even if not, it's not like the throne hasn't been succeeded by someone with no blood relation to the Septims before. Presumably they wore the Amulet, since it didn't trigger any Dagon shenanigans, so it's no real stretch to imagine Martin could too.
What happened to the son Barenziah had by the Nightgale/Jagar Tharn? Could that be Martin? I have seen mention of the name Calaxes (sp?) Septim, another bastard?
Oh, juicy. I don't know how it could work, but I love the idea.