Prince William partied with friends and shouted “I’m free!” after calling off his relationship with Kate Middleton in a frank 30-minute phone call, a royal insider has revealed.

The Prince of Wales, then aged 25, is said to have ended things with the Princess of Wales after deciding he was too young to settle down, Rob Jobson says in his new biography of Kate which details the couple’s brief 2007 split.

It came about after William, who formed a romantic relationship with Kate as an undergraduate student at St Andrew’s University, cooled on future plans for the pair amid speculation he was preparing to propose.

“‘I’m free!’ he shouted as he slipped into a drunken version of the robot dance,” Jobson claimed of the celebration, which took place in Mayfair’s Mahiki nightclub. “He then told his friends that they should all ‘drink the menu’, which they more or less ended up doing.”

According to reports at the time, the Prince also had his eye on someone else, the socialite Isabella Anstruther-Gough-Calthorpe, but she is said to have rejected his advances because she did not want to be constrained by the inevitable demands of royal life.

“This did not cool William’s ardour,” Jobson explained.

“He reportedly tried to woo Isabella, visiting her several times at her family home. Despite his evident crush, she apparently rebuffed his advances.

“Few could have predicted that he’d return to Catherine or that she’d ever agree to take him back.”

At the time of the split, they had been an item for five years, having seen their initial friendship blossom into romance when Kate wore “a daring black sheer ensemble that showed off her figure” at a student charity fashion show in 2002.

By the time the pair graduated, rumours of an engagement were swirling, with some members of the press dubbing the future princess “Waity Kate” because of the length of their relationship without an engagement.

After William had cancelled plans around the time of Kate’s 25th birthday in January 2007, she “sensed something was wrong”.

Jobson wrote: “[William] told her they both needed ‘a bit of space’ to ‘find our own way’, and he was unable to promise her marriage.

“In an emotionally charged 30-minute conversation, they both acknowledged they were on ‘different pages’. It was a devastating blow to Catherine, who felt doubly let down at being dumped over the phone.”

The Duke and Duchess of Cambridge

But Kate’s actions after their break-up reportedly made it impossible for the prince to get his university girlfriend off his mind.

She was helped by her mother, Carole, who took her on a trip to Dublin to distract her from the heartache.

“Carole Middleton acted swiftly, taking her heartbroken daughter for a break in Dublin — a welcome respite from media scrutiny,” Jobson added.

“On Catherine’s return, she decided she wasn’t going to sit around moping; what was good for the goose was good for the gander.”

Now in the public eye, she was repeatedly photographed by paparazzi wearing more risqué outfits than ever before when she went out with friends, and there was one, in particular, that sealed their eventual reunion.

Jobson added: “She turned to old friends for support, going on holiday with a girlfriend to Ibiza. They partied long into the night.

“Back in London, there were soon so many paparazzi shots of Catherine leaving nightclubs — often with her sister Pippa — that the media dubbed them the ‘Sizzler Sisters’.”

This outfit caught William’s eye at a fancy dress party when “[Kate] arrived dressed as a nurse and William had made a beeline for her”.

However, because of their earlier split, their reunion was initially kept a secret, but William did promise to marry Kate.

“He finally proposed formally during a holiday in Kenya in 2010, by the side of the turquoise waters of Lake Alice,” Jobson wrote. “The question wasn’t entirely unexpected, of course, but Catherine’s face lit up with a radiant smile as she said yes.”​