Civilization Leaders Changing mid game?

[zarakand]

In my last few games, I have had a few civilizations change leaders in the middle of the game without having revolutions etc. For example, I was next to the English and their leader was Churchill. There were no revolutions in his lands (that I'm aware of it is possible I missed the message) and then all of a sudden the English were led by Elizabeth.

I didn't realize that this could happen. How does it happen and what are the reasons for it? Thanks!

 

[LastLegionare]

It's a feature, but I haven't noticed AI use it. On the message at start of the game, the key shorcuts that change leader and civ are shown (I don't know them by heart) at the bottom.

 

[Bezurn]

I think this occurs when the empire stability is very bad. I've had this happen to me, I let the other leader take over for a while because I had severely over expanded on a huge map. Quite a few turns passed and I was given back the reins. With the AI it seems that the new leader takes over for good, as I had Russia with Stalin early in the game, and then Mid / Late game I noticed I was talking to Peter now. Never did finish that game, got to 64% on the religious victory, but then everyone got Astronomy