The Terminator star reached the milestone on Thursday (30Jul15), and he celebrated over the weekend (01-02Aug15) by hosting a bash at the Montage Hotel in Beverly Hills, California for pals including Stallone, Sir Elton John, and his ex-wife Maria Shriver.

Stallone documented the bash in a series of messages posted on Twitter.com, sharing pictures of himself with other guests, while he also added a shot which appeared to show him pretending to box with Schwarzenegger.

He added in a caption, "At Arnold's birthday party getting punched out. The man's not getting older, he's getting stronger!"