William and Harry used to join in on Princess Diana's training sessions at the palace

Anyone who's attempted an at-home workout will know there's a high risk of unexpected guest appearances, be they from children or pets.

Princess Diana experienced this too, with her sons Prince William and Prince Harry sometimes joining in on her training sessions at Kensington Palace.

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Jenni Rivett observed the late royal's close bond with her sons during her time as Diana's personal trainer.

"[Her boys] were her whole world and would often join in on our training sessions at Kensington Palace — annoying her occasionally," she tells the Daily Mail.

"[She] would love to embarrass them, too — her sense of humour was one of her greatest traits."

Rivett began working with the Princess of Wales in 1991, a year before her separation from Prince Charles was publicly announced.

The breakdown of her marriage wasn't the only struggle facing Diana at the time; she had also battled with bulimia since the early days of her marriage.

"I just encouraged her with healthy eating and I honestly believe the exercise helped her manage her bulimia," Rivett says.

"I believe as her body became fit, strong and healthy, she felt empowered and ready to face those bad times head-on."

Rivett recalls Diana enjoyed exercise fads like step aerobics, rollerblading and power walking.

The royal was often pictured rollerblading in Kensington Gardens during the 90s.

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Season 4 of The Crown even depicted her skating around the palace during the early days of her relationship with Charles.

In the seven years she trained Diana, Rivett developed a close relationship with the royal.

Two years ago, Rivett put up for auction one of Diana's most famous sweatshirts, which she'd passed on to the trainer a few months before her death in 1997.

She sold the Virgin Atlantic 'Flying Lady' jumper, originally given to the princess by Richard Branson, for a Malawian family based in South Africa.