'Hills' Stars Heidi Montag, Spencer Pratt's Prayers Answered By Mischa Barton

Heidi Montag and Spencer Pratt are huge fans of Mischa Barton ... 'cause they say it's basically divine intervention she's joining them on the reboot of "The Hills."

We got Heidi and Spencer shopping Thursday at Couture Kids on Robertson and asked them about their newest cast member ... and Spencer says he's been praying for Mischa's presence for a loooong time.

It's interesting ... Heidi and Spencer say they never crossed paths with Mischa on the Hollywood party circuit. So, they can't wait to get started working with her on "The Hills: New Beginnings."

As for Mischa ... we got her Wednesday at Craig's in WeHo and she looked thrilled to be crossing over into reality TV.

For those bashing Mischa's career path, save it -- Spencer ain't havin' it!

Just be ready for lots of references to her time starring on "The O.C."

The last time we heard from Mischa, she was being sued for crashing a U-Haul into a building ... so this seems like a better use of her time.