AnimationCollection is there such a thing?!

Question

I wanted to know if there is a way to begin a collection of animations and associate a Completed event for the collection instead of a single animation.

Why?

I'm trying to create a TransitionOut effect this effect needs for a panel to slide down and another to slide up closing in the middle at the same time the background image must fade out, when everything finishes I need the control to close itself.

How can I do this in a clean way?!