Chris Martin Celebrates Birthday with Gwyneth, Tons of Celeb Friends

Chris Martin is consciously celebrating his birthday with his ex-wife and a ton of their famous friends.

The Coldplay frontman hit 42 on Saturday and marked the occasion with a huge bash at his Malibu crib. Of course, Gwyneth was there ... along with Julia Roberts and Sean Penn, who arrived at the same time.

"Shameless" star Jeremy Allen White also showed up for his buddy's Earthday bash. Now, far as we know, Chris didn't have to sing for his cake -- instead, they had a mariachi band to handle the entertainment.

Chris' potential future mother-in-law Melanie Griffith was there too, but interestingly ... no shots of GF Dakota Johnson. Maybe she was somewhere getting ready to jump out of the cake.

And not that there's any question by now as to how tight Chris and Gwyneth still are -- but she also posted a sweet birthday note for him. #ModelExes