Princess Charlotte — who recently saw Taylor Swift in concert alongside her dad, Prince William, and her older brother, Prince George — is the royals’ biggest Swiftie.

“Princess Charlotte is the huge Taylor Swift fan in the family,” a source told “Entertainment Tonight” on Monday.

“She has wanted to go to the concert for months, but with her mum being treated for cancer, this was a really special day to be able to celebrate her Papa’s birthday like this.”

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Princess Charlotte a huge Taylor Swift fan, a source said Monday.via REUTERS

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“She has wanted to go to the concert for months, but with her mum being treated for cancer, this was a really special day to be able to celebrate her Papa’s birthday like this,” the source added.

Charlotte, 9, and George, 10, celebrated their dad’s 42nd birthday Friday at Swift’s first Eras Tour show in London.

William’s wife, Kate Middleton — who announced in March that she was undergoing “preventative chemotherapy” for an unspecified form of cancer — was not in attendance.

Instead, she stayed home with their youngest child, Prince Louis, 6, according to “ET.”

“Charlotte absolutely loved [the concert],” the source said. “They are really wonderful children. William and Kate have done a fantastic job raising all three of them.”

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William’s wife, Kate Middleton — who announced in March that she was undergoing “preventative chemotherapy” for an unspecified form of cancer — was not in attendance.Getty Images

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Instead, she stayed home with their youngest child, Prince Louis, according to the source.Getty Images
After the show, the singer and her boyfriend, NFL star Travis Kelce, had a private meet-and-greet with the royals backstage.

“Happy Bday M8! London shows are off to a splendid start 🇬🇧🇺🇸🤝@princeandprincessofwales,” Swift, 34, captioned a group selfie, a different angle of which the Prince and Princess of Wales captioned, “Thank you @taylorswift for a great evening! #LondonTSTheErastour.”

The source made sure to note that Charlotte and George “understand and appreciate how lucky they are meeting someone like Taylor Swift.”

Meanwhile, an insider close to William insisted he doesn’t mind that his “dad dancing” to “Shake It Off” went viral because he “is focused on his wife and children right now. He really just wanted it to be a special night for Prince George and Princess Charlotte.”

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“Charlotte absolutely loved [the concert],” the source said. “They are really wonderful children. William and Kate have done a fantastic job raising all three of them.”Getty Images

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After the show, Swift and her boyfriend, Travis Kelce, had a private meet-and-greet with the royals backstage.Instagram/@taylorswift
Last weekend, Middleton, also 42, attended Trooping the Colour — her first public outing since revealing her cancer diagnosis.

“I’m looking forward to attending the king’s birthday parade this weekend with my family and hope to join a few public engagements over the summer, but equally knowing I am not out of the woods yet,” she said in a statement ahead of the gathering.

“I am learning how to be patient, especially with uncertainty. Taking each day as it comes, listening to my body and allowing myself to take this much needed time to heal.”

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The source made sure to note that Charlotte and George “understand and appreciate how lucky they are meeting someone like Taylor Swift.”Getty Images for TAS Rights Management

Although Middleton assured fans that she’s been “making good progress,” she explained that she still has “good days and bad days.”

“On those bad days, you feel weak, tired and you have to give in to your body resting,” she shared. “But on the good days, when you feel stronger, you want to make the most of feeling well.”

She added that “treatment is ongoing and will be for a few more months.”