'One of the scariest moments': Prince William opens up about 'overwhelming' experience of becoming a father

Prince William found the reality of becoming a parent "overwhelming" after losing his mother at a young age, the British royal has revealed in a new documentary.

The Duke of Cambridge, 37, admitted that starting a family "is the biggest life-changing moment" in conversation with English footballer Marvin Sordell.

The third-in-line to the British throne stars in Football, Prince William and our Mental Health, a BBC documentary that will release on Thursday, May 28.

In the programme, the royal meets players, managers and fans in an effort to promote the importance of mental health in the sport.

During his meeting with former Premier League footballer Sordell, who grew up without a father, Prince William revealed becoming a dad brought back emotions he felt after his mother's death.

The royal was 15 when Diana, Princess of Wales, was killed in a car crash in Paris.

"When you have been through something traumatic in life – and that is like you say your dad not being around, my mother dying when I was younger – your emotions come back in leaps and bounds because it's a very different phase of life," Prince William candidly said in the documentary, according to the BBC.

"And there is no one there to help you, and I definitely found it very, at times, overwhelming."

Prince William has three children with Catherine, Duchess of Cambridge: Prince George, 6, Princess Charlotte, 5, and Prince Louis, 2.

Prince William also opened up about how he and Catherine, 38, approach parenting, revealing they "evolve and learn together".

“Me and Catherine, particularly, we support each other and we go through those moments together," he said. “I can completely relate to what you are saying about children coming along – it’s one of the most amazing moments of life, but it’s also one of the scariest.”

Earlier this year, the Duchess of Cambridge revealed the two try to instil a love of the outdoors in their children.

"It's so great for physical and mental well-being and laying [developmental] foundations," she said in an episode of podcast Happy Mum, Happy Baby in February. "It's such a great environment to spend time in, building those quality relationships without the distractions of 'I've got to cook' and 'I've got to do this.' And actually, it's so simple."