“She puts her hand on my arm, looks me in the eye, and says, ‘Come on, William. Let’s go and sing,’ ” William recalls of the memorable moment

Prince William is opening up about his famous duet with Taylor Swift for the first time, admitting that he “got up like a puppy” when persuaded by the singer.

Back in 2013, the royal was led to the stage by Swift during a Centrepoint charity event at Kensington Palace to join Jon Bon Jovi for a rendition of “Livin’ on a Prayer.’ ”

The impromptu concert was described by William’s aides at the time as completely “off the cuff.” Now, eight years later, William is revealing how the memorable moment went down on a special Christmas episode of Apple Fitness+’s Time to Walk series, which premieres on Dec. 6.

“So, around about – it must be nearly 10 years ago now – I can’t believe I’m actually telling this story. I went to a charity fundraising gala for Centrepoint, which is a young homeless charity that I am very fond of and have supported for many years. It’s an annual fundraiser, and I turn up, and Jon Bon Jovi and Taylor Swift are at the event, which nearly knocked me off my feet, as well,” Prince William says.

“When I sat down to watch Jon Bon Jovi do his performance, I thought, ‘That’s it. My job is done. I’ll get a dinner in a minute, and I might be able to have a chat to some people, and, you know, I’m off-duty a little bit now.’ Little did I think what was going to happen next,” he continues.

“I’m sat next to Taylor Swift. She’s on my left. And after Jon does his first song, there’s a pause, and she turns to me. She puts her hand on my arm, looks me in the eye, and says, ‘Come on, William. Let’s go and sing,’ ” he recalls.

“To this day, I still do not know what came over me. Honestly, even now I’m cringing at what happened next, and I don’t understand why I gave in. But, frankly, if Taylor Swift looks you in the eye, touches your arm, and says, ‘Come with me…’ I got up like a puppy and went, ‘Yeah, okay, that seems like a great idea. I’ll follow you.’

“I walked up on stage in a trance, and then sort of halfway through Jon Bon Jovi’s “Livin’ On a Prayer” song, I wake up,” he says. “And I’m thinking to myself, ‘Am I standing on the stage singing ‘Livin’ On a Prayer’ when I don’t even know the words?’

“But the Centrepoint young guys and girls were there all loving it and cheering away. So I thought, ‘Well, if they’re enjoying it, then the night is for them. So sod it. I can’t be the doofus who’s going to ruin it for everyone.’

“And so I desperately try and remember some of the words and sing as hard as I can. Beneath my black tie, there was a lot of sweating going on. I felt like a swan, where I was trying to keep myself composed on the outside, but inside, the little legs are paddling fast.”

William then admits that despite his experience in front of crowds and on stage, he wasn’t prepared to put his vocal skills on display.

“Now, a lot of people might think that I’m comfortable on stage. When I do speeches and things like that, I’ve done so many now, they’re not a problem. But I’ve not done singing,” he reveals. “At times, when you’re taken out of your comfort zone, you’ve got to roll with it.

“And I think we’ve gotten to the stage in this life where we do micromanage ourselves. We do worry about: how do we look on social media? Who said what about me? What am I wearing? There’s so many pressures, but I think making a fool of yourself is okay.

“It’s okay to not take yourself too seriously and have those moments where you let go and you just go, ‘Do you know what? I’m okay with this.’

“So, yeah, go on and have a laugh. And don’t go and watch the video of me singing. Or do go and watch it, but just laugh to yourself about how I was feeling.”

Earlier this year, Willam teamed up with Apple Fitness+ to record one of their inspiring audio walking experiences, which features personal stories from influential people to inspire users to walk more. He approached Apple to take part as he was impressed with Time to Walk and how it coincided with his efforts to promote better mental health and wellbeing.

Prince William’s walk takes him through the Queen’s Sandringham Estate in Norfolk — from Sandringham House, past St. Mary Magdalene Church and ending eventually in Anmer, where William and his wife Kate Middleton have a country home.

Recognizing the significant impact that walking has on mental health and that the holidays can be challenging for many, William has chosen three charities to receive a five-figure donation from Apple: Shout in the UK, Crisis Text Line in the USA and Lifeline in Australia. Crisis Text Line and Shout provide free, 24/7 confidential support for people in crisis via text, and Lifeline provides free, 24-hour confidential crisis support and suicide prevention services.

Apple will stream three special audio airings of the Time to Walk episode for free on Apple Music 1, the flagship global radio station on Apple Music, on Dec. 6.