As with most PC versions of games, there will eventually be funny and odd mods that players can play around with and it looks like the modders managed to discover something interesting in the game.
DaniMoz, a user in Reddit discovered that players can use mods to play as Princess Isabeau Katharine Zonsmeister as she is in the game files which will allow modders to play with her. If you are not familiar with the game, she is actually a character in the game that has been missing for 15 years. She is not seen in the game but it looks like Rockstar might have more planned for her.
To control her, you will need to use the Lenny’s Simple Trainer mod and type CS_PrincessIsabeau into the “models” line in the Ist.ini file of the mod.
We still do not know why she is in the game but maybe we will see something from Rockstar soon.