Got a mate in the Immortal faction who wants to invite me.
However I am currently in the Shadow Faction.

Is it possible to switch sides and if yes, how?

Thanks in advance

Once you become a shadow you can not join Immortal. Even if you leave your shadow clan. I found this out as a clan leader for immortal. I slowly realize that this is a way for them to make sure immortals dont reign forever. Shadows have a pool of people to work with forever. Immortals slowly start losing higher level CR because they get sucked up by shadows. The way they did the PVP / CVC in this game is quite genius tbh.

Cheers for the quick and complete response mate.
Will have to wait for the next cycle

It's a really unique thing in the game which I like alot, even if it is very confusing at first