The British royal is said to have gone clubbing with socialite Cressida Bonas until 4am on Wednesday (July 18), reports The Sun.
Prince Harry had attended the UK premiere of The Dark Knight Rises earlier in the evening, before heading to an afterparty in Camden.
After leaving the party at 2am, his entourage went to Le Salon club in Mayfair, where he was seen chatting to Bonas for the rest of the evening.
Bonas reportedly attended the same university as Harry's ex-girlfriend Chelsy Davy.
"Harry and the group danced their socks off but he was never far away from the stunning blonde," a witness said. "At one point he was sitting down playing with her hair before finally leaving just after 4am.
"The girls came out first and Harry emerged about five minutes later. She and Harry got into different cabs though, and obviously went their separate ways."
Bonas is the daughter of social figures Jeffrey Bonas and Lady Mary-Gaye Georgiana Lorna Curzon.
Prince Harry had been spotted on a date with a mystery blonde woman earlier this year.
Watch Digital Spy's video from The Dark Knight Rises premiere below: