Restless crowns: forging empires [Late era -Skip a few]

[sonnet]

He killed the pope.As far as i know if you kill the pope the crusade ends (i believe that is the purpose of this rule) but i am not sure if it ends too if the pope is killed by the muslim faction.

Killing is not the same as assassinating. Assassinating is a specific method of killing (and within the game you do that with assassins only).
I forbid in the rules that assassinating the Pope once the Crusade is called, because as you said the crusade is cancelled if the Pope dies.
But that's only true if the crusade is called against a Catholic faction (and as long as the Catholic faction is not at war with the Papal State)

So it won't work if the crusade is called against a muslim faction: the crusade is still on.
There's no way for a muslim faction to cancel a crusade once it's called against it.

But in any case, the rule says assassinate, not killing. Are 2 different things .