"That's certainly a central piece to it. But... it's a hard question to answer," the royal said.
Prince William and Kate Middleton released the black-and-white photo on the prince's 11th birthday on Monday.
The Prince of Wales attended Taylor Swift's show, where he met up with the two football players backstage.
The palace honored Swift with a brass band cover of her 2014 hit "Shake It Off," before she posed with royalty and performed in front of nearly 90,000 fans.
The new photo comes just one day after the Princess of Wales made her first public appearance in six months.
And it has nothing to do with the health of the royals.
The Princess of Wales revealed on March 22 that she had been diagnosed with an unspecified kind of cancer.
The Princess of Wales announced on March 22 that she had been diagnosed with an undisclosed form of cancer.
The Princess of Wales said in March that she'd been diagnosed with cancer following abdominal surgery.
The Prince and Princess of Wales celebrated 13 years of marriage on Monday.
