Groo's first encounter with The Witch of Kaan was in the tale called "The Turn of The Wheel". Groo traded the Witch's Glass Eye for the Claw of Mulamar, in order to complete a quest to rescue The Sage.
Then in the tale of "Groo and the Witches of Brujas", Groo is once again on a quest to find the Glass Eye. This time to return the Glass Eye to the Witch of Kaan.
The Witch of Kaan was last seen rejoicing in Groo's supposedly funeral.