One of the cards allows you to redirect attacks. Is it possible to redirect someone to a player that he is 'supporting'?

Thank You!

I assume you're talking about the Title cards, specifically the Crown Regent. When using that title, the attacking player (not the player using the Crown Regent) chooses the new defending player. And they can indeed go against the player they're supporting. Also, the attacking player can choose new targets for Stealth. You'll find the detailed explanation in the Rules Reference Guide, under "Redirect".

Alright thx!

You're welcome.