We’ve known since early this summer that Emma Thompson would not appear in the next Harry Potter sequel as Sybill Trelawney. What we didn’t know, until now, is why.

Speaking to MTV, Emma revealed that leaving Harry Potter was her decision. Forced to choose between doing Potter and doing a sequel to her somewhat poorly received 2006 fantasy movie Nanny McPhee… she went with McPhee.

According to Thompson, it came down to which she cared about more. She says, “I’m making my own ‘Nanny McPhee’ next year. They mean much more to me.” It’s great that she’s got a project she’s so passionate about. Unfortunately, I’m not really sure anyone else is equally excited about it.

Does the world really need Nanny McPhee 2? She thinks so, and wants you to know it won’t really be a sequel. Says Emma, “The working title is ‘Nanny McPhee and The Big Bang. It’s not a sequel, actually, it’s a new story.”

The original Nanny McPhee was basically Mary Poppins with warts. Thompson put on all kinds of prosthetics to play a take no prisoners, magical nanny who moves into a household and teaches the kids there… whatever important lessons it is that kids learn from nannies. Mary Poppins taught them this by dancing on the ceiling, Nanny McPhee teaches it by doing things like dropping the baby in a pot of boiling water. No, really.