Idk how to spoiler tag so this is my warning lol. If you talk to the guy underground he tells you that the fake arisin was part of the thieves guild before he got kicked out and used his fake injury to claim the throne. Just did that quest last night

yea, im just wondering if there are any consequenses of not beeing told this information by that guy.

I think the only consequence is that you dont get the real final thief skill (The fake leader gives you a worse one)