Justin Bieber Parties With Justin Bieber

Justin Bieber got down with the fastest man on Earth to celebrate a movie about the Olympian ... and he was anything but sorry to be partying with the champ.

Bieber was in London Monday night and showed up to an after-party following a screening of "I Am Bolt" -- a documentary about Usain Bolt's journey to the Rio Olympics.

Unclear if the Biebs saw the film itself, but he definitely raged with the man of the hour afterward.

One Direction's Liam Payne was there for the screening and party too, but was reportedly on the opposite side of the room ... meaning he missed out on the Bolt/Bieber selfies.