What is the Warmonger penalty for a Joint War?

Normally when you are looking at declaring war you get a tip telling how severe your Warmonger penalty will be for this declaration.

However, when an ally asks you to declare a Joint War, you get no such information (or at least I failed to spot it).

The last time I did this I immediately received a denouncement for being a warmonger, so I assume there is a reasonably high warmonger penalty for it?

Does anyone know how big this penalty is? Is it based on the Casus Belli of the ally asking you to join? Is it just the standard Formal War penalty?


The Civilization VI ‘Fall 2016’ seems to have changed how the Warmonger penalty works:

"Reduced Warmonger penalties in most instances, and adjusted how this reacts to returning versus keeping a city. The last city conquered from a player now provides a heavy warmonger penalty, even if you have a Casus Belli against this player, because you are wiping out a civilization."

and

"Players will no longer receive any warmongering penalties from a joint war partner for actions in that joint war."

https://civilization.com/news/entries/civilization-vi-fall-2016-update-now-live