Princess Charlotte – who recently saw Taylor Swift in concert with her dad Prince William and big brother Prince George – is the royal family's biggest Swiftie.
“Princess Charlotte is the biggest Taylor Swift fan in the family,” a source told “Entertainment Tonight” on Monday.
“She has been wanting to go to the concert for months, but her mum is undergoing cancer treatment, so being able to celebrate her dad's birthday in this way was really special to her.”
Charlotte, 9, and George, 10, celebrated their dad's 42nd birthday at Swift's first Eras Tour show in London on Friday.
William's wife, Kate Middleton — who announced in March that she was undergoing “preventive chemotherapy” for an undisclosed type of cancer — was not in attendance at the ceremony.
Instead, she stayed home with her youngest child, 6-year-old Prince Louis, according to “ET.”
“Charlotte loved it [the concert]”They really are wonderful kids. William and Kate have done a fantastic job raising the three of them,” the source said.
After the show, the singer and her boyfriend, NFL star Travis Kelsey, had a private meeting with the royal family backstage.
“Happy Birthday M8! The London show is off to a great start 🇬🇧🇺🇸🤝@princeandprincessofwales,” Swift, 34, captioned a group selfie, which featured the Prince and Princess of Wales at a different angle, captioning, “Thank you @taylorswift for a great evening! #LondonTSTheErastour.”
The source also revealed that Charlotte and George “understand and appreciate how lucky they are to have someone like Taylor Swift by their side.”
Meanwhile, a source close to William insisted that he doesn't mind that his “father's” dance to “Shake It Off” went viral because he is “focused on his wife and kids right now. He really wanted it to be a special night for Prince George and Princess Charlotte.”
Last weekend, Middleton, 42, attended Trooping the Colour — her first public event since revealing her cancer diagnosis.
“I am looking forward to joining my family in the King's Birthday Parade this weekend and hope to attend some public events over the summer, but know that I am not out of the woods yet,” she said in a statement ahead of the ceremony.
“I'm learning to be patient, especially during times of uncertainty. To take each day as it comes, listen to my body, and give myself the time I need to heal.”
Though Middleton reassured fans that she's “making good progress,” she revealed that she still has “good days and bad days.”
“On bad days you feel weak and tired and you need to give your body a rest,” he explains. “But on good days, when you feel strong, you want to take full advantage of feeling good.”
He added that “the treatment is ongoing and will go on for a few more months.”