Justin Bieber has donated $545,000 towards HIV research at the amfAR gala charity ball in Cannes on Thursday.

The event was hosted by Hollywood mogul Harvey Weinstein and guests included Sharon Stone, John Travolta, Leonardo DiCaprio and Heidi Klum.

Another donor at the event made a $545,000 donation and Bieber quietly offered to match it.

Organisers were floored by the offer and had to double-checked with Bieber to make sure he was serious about the donation, which he confirmed he was.

$51 million dollars was raised towards AIDS funding and research.

He subsequently took to his Twitter page and wrote, "Amfar #giveback". 

Amfar #giveback

— Justin Bieber (@justinbieber) May 22, 2014