Brad Pitt poked fun at Rihanna and Jay Z at the Diamond Ball last night (11.12.14).

The 'Moneyball' actor introduced the 'We Found Love' singer's performance at her charity bash in Beverly Hills with a mocking speech about ''what the f**k went wrong'' for the 26-year-old star.

An old photo of Rihanna appeared on a big screen as Brad said: ''I've often asked the very questions you yourself are asking right now - what the f**k went wrong?

''I give you exhibit A. Look at the young girl before you, all full of hopes and dreams, living a humble existence in Barbados, her whole life ahead of her.''

He then recalled how Rihanna moved to New York when she was just 16 years old but ''soon fell in with a bad crowd led by the dubious and nefarious character known as The Jay Z.''

He added to laughter from the audience: ''For those you not in the know, The Jay Z was an evil impresario known for turning out hit records and ripping insane lyrics and fresh beats.

''Needless to say it was all downhill from there.''

The 50-year-old star went on to list Rihanna's accomplishments, award wins and record sales but pleaded with the crowd to stage an intervention as an altered image of the 'Diamonds' hitmaker overweight and eating a sandwich appeared on the screen.

He said: ''I ask that we stand together by her side and show her our support and our love and say to her the hard words, 'Rihanna put down that sandwich, get off your ass and do something. God damn it, just do something with your life.' ''

Rihanna then stepped out onto the stage and performed her medley of hits backed by a live orchestra for the guests, which included Lewis Hamilton, Kim Kardashian West and Kris Jenner.

Jimmy Kimmel hosted the event, which raised money for Rihanna's Clara Lionel Foundation.

A live auction saw Salma Hayek pay $190,000 for a piece of Damien Hirst's artwork, while four VIP tickets to an upcoming Kanye West show went for $74,000.