Prince William reveals 'cringing' moment with Taylor Swift, some of his favorite tunes and car rides with his mom and Harry

Prince William walks near St. Mary Magdalene Church on the Sandringham Estate in Norfolk.

London (CNN)The Duke of Cambridge will take listeners on a walk down memory lane when he joins forces with Apple Fitness+ for a special festive episode of its "Time To Walk" audio series.

William, 39, is hoping to encourage people to take a break and go for a walk for their mental wellbeing over the Christmas period. CNN understands the duke is a fan of the series and approached Apple about the project.
William opens the episode contemplating his father's love of walking and that while growing up, Charles "used to try and force Harry and I out of the house the whole time" adding that "we weren't really having any of it."
    "But now, as you get older, you appreciate it a lot more and you see it for what it is," William says.
      The royal is the latest star to record a walk-and-talk for the series, available on Apple Watch with a Fitness+ subscription.
        Each episode, which ranges between 25 and 40 minutes in length, is designed to be an immersive experience. Featured guests take a stroll in a meaningful location and reflect on life's lessons while sharing memories and experiences through stories, photos and songs.
        The Duke of Cambridge talks in the podcast of the importance of keeping mentally fit.
        William's walk -- which he recorded back in the spring -- takes him across his family's sprawling 20,000-acre Sandringham Estate in Norfolk, eastern England. Starting at Sandringham House, he takes in the sights and sounds of "the great British countryside, as we like to call it" while heading towards St. Mary Magdalene Church, where the royals are due to attend Christmas Day church service later this month. He ends the journey standing outside Anmer Hall, the home he shares with wife, Catherine, and their children.
          Reflecting on his family's annual Christmas Day pilgrimage, William talks of his "strong memories" of his grandfather plowing ahead while "there'd be us at the back with little legs trying to keep up."
          During the episode, the prince discusses the importance of keeping mentally fit and recalls one moment nearly a decade ago that left him sweating at a black tie event.
          Musing that he "can't believe I'm actually tell this story," he talks about a 2013 fundraising gala at Kensington Palace that US singers Jon Bon Jovi and Taylor Swift attended, "which nearly knocked me off my feet."
          Prince Charles,  Catherine, Duchess of Cambridge, Princess Charlotte of Cambridge (unseen), Prince William and Prince George arrive for the royal family's traditional Christmas Day service at St. Mary Magdalene Church in Sandringham, Norfolk, eastern England, on December 25, 2019.
          William says there's always "a lot of handshaking to do those nights" where he tries to "be charming and interactive." He then goes to watch the performance thinking his main tasks of the evening -- primarily to welcome guests -- are over and he can relax a little.
          "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 remembers.
          "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.'"
          William continues his anecdote describing walking towards the stage "in a trance" and trying to desperately remember the lyrics to "Livin' On a Prayer."
          The Duke of Cambridge sings with Taylor Swift and Jon Bon Jovi at the Centrepoint Gala Dinner at Kensington Palace in London, on November 26, 2013.
          "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," the royal says, adding that while he's very comfortable delivering speeches, he has less experience singing live.
          "At times, when you're taken out of your comfort zone, you've got to roll with it," he adds.
          During the episode, the duke also reveals the impact his time as an air ambulance pilot had on his mental health. He details one experience helping a young boy hit by a car.
          William says he "went home that night pretty upset but not noticeably" and was conscious that "something had changed... a real tension inside of me." He describes compartmentalizing his feelings and returning to work but "it really hit me weeks later."
          "My personal life and everything was absolutely fine. I was happy at home and happy at work, but I kept looking at myself, going, 'Why am I feeling like this? Why do I feel so sad?' And I started to realize that, actually, you're taking home people's trauma, people's sadness, and it's affecting you."