What will go down this Sunday on Keeping Up with the Kardashians Season 9?

That's what Khloe and Kendall want to know!

In the following sneak peek at the upcoming episode, we're on a private plane with various family members as they fly to San Francisco because Kanye West has some birthday surprise in mind for Kim.

What could it be?!? We all know the answer at this point, of course.

But check out the clip to see the siblings wonder about it and then watch Keeping Up with the Kardashians Season 9 online to catch up on anything you've missed:

Matt Richenthal is the Editor in Chief of TV Fanatic. Follow him on Twitter and on Google+.