From The Grey House, Book Three, Protector of the Grey House:
Natalia was once again lying with her back to Vincent’s chest, considering all that had transpired while her man was gone. She told him of her days without him, informing him of Franklin’s betrayal and death, to which he grew contemplative, finally stating that he should have known. She didn’t question why and he didn’t elaborate. It wasn’t his way and she didn’t need to pry. There was something she did want to know about, though.
“Vincent? Who was the ghul in the oubliette?”