Brit's Bummed About Leaving Her Boys Behind!

Now we know why Britney looked so sad last night!

A little over an hour ago, the pop princess boarded a flight from LAX to Frankfurt, and it looks like she's down in the dumps about leaving sons Sean Preston and Jayden James behind.

As you may already know, Brit is headed overseas to promote her new album, Circus. She'll be performing on The X Factor and Star Academy next week, and then she's coming back to the U.S. to perform on Good Morning America on her birthday. Sean Preston and Jayden James need not worry too much - looks like mama will be back soon enough!