Prince William has grown in confidence and strength as a father figure, especially with Kate Middleton’s recent cancer diagnosis…

Prince William won major dad points when he brought son Prince George, 10, and 9-year-old daughter Princess Charlotte to Taylor Swift’s June 21 concert at London’s Wembley Stadium. (Prince Louis, 6, either not a Swifty or more likely just too young, stayed home.) The kids were thrilled to meet the singer, 34, as well as her boyfriend, Travis Kelce, and his brother, Jason, backstage, where the heir to the throne, 42, made quite an impression on the NFL players. “We met royalty, guys,” Travis, 34, gushed on the brothers’ New Heights podcast, saying of William, “Dude, he was the coolest motherf–ker. He was so cool.”

Not exactly Buckingham Palace–approved language, but apparently in the wake of his wife Princess Kate’s cancer diagnosis and ongoing chemotherapy, the Prince of Wales has more than stepped up for their children. “He says he’s a changed man,” a palace insider exclusively tells In Touch. “He’s shouldered a lot of the responsibilities, and, what’s more, he seems to be having fun doing it. Kate has seen the change, and she’s genuinely touched by all that he’s doing, not just for her, but for the children.”

When Kate and William wed on April 29, 2011, the pair exchanged traditional vows. “For better, for worse, for richer, for poor, in sickness and in health,” they each pledged. Kate’s cancer at age 42 has made those words all too real. “It forced her and William to take a good look at their priorities and be more grateful for what they have,” says the insider. “Their vows have never been more profound as they navigate this difficult time.”

While Kate managed to appear with the royal family to celebrate King Charles III’s birthday at the June 15 Trooping the Colour, her health is uncertain. In a recent message, the Princess of Wales shared that she has “good days and bad days. On bad days you feel weak, tired and you have to give in to your body resting.”

It’s comforting to see her husband fully embracing fatherhood. “He was already hands-on,” notes the source. “But he’s become more confident and stronger in his role as dad. It’s reassuring for Kate to know the kids will always have a loving, compassionate and caring relationship with their father if, God forbid, something happens to her.”

Having lost his beloved mother, Diana, at age 15, William seems especially driven to keep things light for his children — even if that means goofily dancing to Taylor Swift. “The kids can sense he’s having fun,” says the insider. “And they’re happy and secure as a result.” In a way, he’s channeling Diana, adds the source. “She was so much fun to be around. She encouraged her kids to play and express themselves.”

After her death, things were different for William and his now-estranged brother, Harry, growing up with Charles (now battling cancer himself). “Single parenthood? Pa was never made for that,” Harry wrote in his memoir, Spare, while the insider calls the monarch “standoffish.”

William has become anything but. “William feels a responsibility to show that he’s evolving and modernizing with the times,” says the insider. “It’s not a burden to him, it’s a privilege.”