Prince William Leaves Hospital ...

Soon-to-be dad Prince William just took a big breather today in London, finally exiting the hospital where his preggo wife Kate Middleton is being treated for severe morning sickness.

William left the King Edward VII hospital moments ago with his royal entourage. The guy's been there since Kate was admitted earlier today.

As we reported, the Royal Palace made the big announcement this morning -- Kate is in the "very early stages" of pregnancy.

It's like a real-life fairy tale! Only with a lot of vomiting.