She's certainly no stranger to the club scene, but Kate Middleton may have misjudged how much she could handle while celebrating Nelson Mandela's 90th birthday bash.

The girlfriend of Prince William looked glamorous and fresh at 8pm while enjoying drinks with friends, where she mingled in the VIP tent.

But just four hours later, as she left the Whisky Mist nightclub at midnight, her face was showing the strain of a not-very-late night of partying.

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...Looking a bit worse for wear four hours later, Kate leaving the Whiskey Mist nightclub

Kate showed her down-to-earth nature by leaving the Mandela's VIP section to mingle with the public front-of-stage, but she and her 11 friends quickly scarpered back to the safety of the velvet ropes when photographers spotted her.

One onlooker said: 'Kate wanted to be at the front of the stage watching the concert with the people as it was more fun than being stuck backstage.

'The group were dancing and singing along all night.'

But as Simple Minds took to the stage, the 26-year-old appeared unsure who they were. 'Did they say Superman?' she asked.

Later the party moved to the Park Lane nightspot but by midnight, Kate was ready to leave, looking tired and worn-out.