Kris Marshall is
absolutely guaranteed confirmed to be the Thirteenth Doctor nothing more than a dedicated family man.
Kris Marshall is most famous for being in a bunch of BT adverts, although Americans probably know him as the English guy who goes to America to see if having an accent will help him pick up chicks in that Love, Actually movie that their girlfriend (>implying) dragged them to see in 2003.
He's also the only British actor alive who's never appeared in anything related to Doctor Who. Seriously, he doesn't even have a page on the TARDIS Data Core Wiki, and they even have a page about you.
First Irish Doctor
We've had English Doctors, Scottish Doctors, other-parts-of-England-English Doctors, why not an Irish one?
Even though Kris is from England, has a southwest English accent, went to CoE schools, and has no Irish ancestry, /who/ is convinced he will be a great first Irish Doctor.
/pol/ demands an early-30s alt-right white male Doctor instead of some cuck midlife-crisis whiny old man, so they're overjoyed with the 43-year-old feminist Labourite Kris Marshall.
Kris quit his current show to spend more time with his family,
causing a run of speculation on Twitter that maybe he was quitting to do Doctor Who instead, causing a run of bets on him as the next Doctor at the online bookies, who quickly suspended betting (until betting resumed two days later and his odds began to slowly go back down).
This absolutely confirms beyond a shadow of a doubt that he has already been cast. The same way that betting being suspended on the 11th Doctor confirmed that it was Paterson Joseph was cast as Eleven, and that the first two times betting was suspended on the 12th Doctor confirmed that it was that other guy whose name I can't even remember, then Paterson Joseph again.
Then Radio Times wrote (and pulled) an article implying that episode 12 might be a regeneration episode, but they'll have to do later inserts for the new Doctor because he's not cast yet. Which means that Kris quitting his show in time for filming of episode 12 proves that he has been cast.
Turns out he was telling the truth about his family.