San Francisco: Jennifer Aniston could be engaged to a love cheat! Justin Theroux was spotted getting affectionate with an attractive blonde, even sharing an embrace with a mystery woman at Cavallo Point on San Francisco Bay, where Robert Downey Jr. threw a weekend-long back for his wife, movie producer Susan, to celebrate her 40th birthday. “He gave her a friendly kiss and a hug when she walked up, which is normal but what was abnormal was the fact that they were stood around with their arms around each other,” a source said.

Guests at the party also included Gwyneth Paltrow, Reese Witherspoon, Jason Bateman and Gwen Stefani. Aniston stayed at home.–SS