In the photo, the Blurred Lines singer’s hand can be seen on the girl’s bottom in the reflection of the mirror behind them.
Twitter users sent the photo to the 36 year-old’s wife Paula Patton, with whom he has a three-year-old son.
'Look at the reflection girl,' warned the sender.
The girl in the photo has been revealed as student and socialite Lana Scolaro by a UK newspaper. She is said to be a student at a New York arts University.
It is thought that the suspicious snap may have been taken at an MTV VMAs after-party in New York - the night of the singer's controversial performance with Miley Cyrus. Robin’s wife was reportedly also at the party.
Robin and Miley’s performance at the awards was criticised for how raunchy it was – with Miley grinding on the R&B singer’s lap.
At the time, it was reported that his wife Paula had been ‘fine’ with the on-stage antics, having allegedly known exactly what was going to happen prior to the show because she had been to the rehearsals.
Robin and Paula began dating 20 years ago, when the budding singer was just 16. The couple went on to marry in 2005 and welcomed their son Julian Fuego Thicke in 2010.
Although Paula might have remained calm about her husband’s VMA’s duet, Robin’s mother Gloria publicly announced her disapproval of the performance .
She said: 'I don't understand what Miley Cyrus is trying to do. I just don't understand. I think she's misbegotten in this attempt of hers. And I think it was not beneficial.’