Newspaper reports say the celebrity couple got back together after Justin phoned Britney and "begged" her to take him back.
Rumours of the showbiz split emerged in March this year, but were at first denied.
Britney admitted she was no longer in an "intense relationship" while promoting her movie, Crossroads, in London.
Mates since Mickey
The break-up was blamed on their difficult work schedules.
Britney and Justin have been mates since they danced around in Mickey ears on the Disney TV show, The Mickey Mouse Club, back in 1993.
Hear story
Chat about music
Vote: find Britney a new man!
Try our Britney quiz
