MEGAN FOX & BRIAN AUSTIN GREEN SEPARATED

Megan Fox and Brian Austin Green have separated after being together 11 years.

The couple married in 2010 and has 2 sons together.

Us Weekly, which broke the story, cites sources saying the decision to separate was made 6 months ago. They've rarely been seen together in public over the last several months ... the last time was back in June.

No word on whether they've decided to file for divorce yet. 

This was the first marriage for both of them -- although Brian had a son with his previous longtime GF, Vanessa Marcil.