One Love Manchester
Will.i.am performs with Ariana Grande at the One Love concertBBC

Willi.i.am has been slammed on social media after he shouted out 'What's up London?' to the crowd at the Manchester One Love concert.

The Black Eyed Peas singer took to the stage at the Old Trafford cricket ground on Sunday evening for a performance of his 2001 hit Where Is The Love with Ariana Grande.

His shout out to London left viewers baffled prompting many to turn to Twitter to point out the faux pas.

"Will I am: 'what's up London?' At a show called One Love Manchester. Incredible," said one incredulous viewer.

"will.i.am you had one job," said another mocking the star. And while he had already caused offence with his gaffe, in a speech at the end of his set he thanked the police 'here in London'.

"I still haven't recovered from Will.i.am thanking the police force 'here in London' said one viewer.

Another wrote: "Someone needs to tell Will I Am he's in Manchester and not London."

Reacting to the backlash The Voice judge tried to explain himself saying: "There was an attack in London last night...I was paying homage and showing love to London and Manchester."

"That's not awkward that's love.. I also thanked the police in Manchester & both Mayors...everyone needs love during attacks of hate," he added.

Some of the world's biggest music stars joined the people of Manchester in a display of defiance and unity at the One Love concert in tribute to the victims of the Manchester Arena terror attack.

Justin Bieber, Katy Perry, Coldplay, Pharrell Williams, the Black Eyed Peas, Usher, Robbie Williams, Take That, Little Mix and One Direction star Niall Horan all performed in a rousing show of support for the people of Manchester.

An emotional Ariana had vowed to return to Manchester after suicide bomber Salman Abedi killed 22 people at her Dangerous Woman concert on 22 May. Applauding the crowd she said: "The kind of love and unity that you're displaying is the medicine that the world needs right now. I wanna thank you for coming, I love you so much. Thank you."