Locked Out Of Heaven Bruno Mars Download 'Locked Out Of Heaven' on iTunes
'Greatest Day' debuted at number one in the UK and became the band's 11th number-one single.
The boys premiered the track at the 2009 BRIT awards and it's now gone on to sell over 400,000 copies.
The music video was filmed on-location in downtown Los Angeles, on-top of a 60-storey building.
It was directed by Meiert Avis, who has previously shot videos for the likes of U2, Bruce Springsteen and Bob Dylan.