U2 reunited for a surprise gig at Sean Penn's Help Haiti Home benefit gala on Saturday night (Jan 11th).

The Montage Hotel in Beverly Hills hosted the iconic band's first live show in four years.

And the biggest names in Hollywood were there to enjoy it, guests included Gwyneth Paltrow and husband Chris Martin, Julia Roberts and Danny Moder, Kevin Bacon and Michael Douglas, plus many more.

The band only played a three song set but it included U2's earlier hits 'I Will Follow' and 'Desire' and 2004's 'Vertigo'.

According to The Hollywood Reporter, Bono told the small audience of 300, "It's been a while since we played a hotel lounge," when they got on stage around 10.30pm. "I think the last time was a bar mitzvah."

The whole night managed to raise almost $6 million for the J/P Haitian Relief Organisation which will provide medical care, water, food and began to rebuild housing that the devastating earthquake destroyed in 2010, People reports.

"This town has been very supportive of me and, more importantly, what our organization is doing in Haiti," Penn tells the mag. "I got a lot of gratitude and no complaints."

Haitian native Anaelle Jean-Pierre was also on hand to sing a rendition of the song 'Hallelujah', but the crowd nearly erupted when Bono joined her for a duet.

During the benefit gala Penn also took to the stage to give the audience an insight into what his organisation has done and what their donated money will be used for.

"When I first arrived after the earthquake, we were managing a camp of 60,000 people. It was the biggest camp in Port Au Prince," Penn said. "To know all those people are in homes and have been relocated because of our program ... to walk through that now piece of land that used to be wall to wall tents, that was pretty moving."

U2 took to stage to perform a surprise gig