His Royal Highness Prince George turns 1 Tuesday, a celebration being marked by the palace with the release of the young royal’s first official solo portrait.

“Look who’s walking!” Clarence House posted to Twitter Saturday with an image of George, the son of the Duke and Duchess of Cambridge, Prince William and Kate Middleton, taking a few steps. “Here’s our little Prince ahead of his 1st birthday on 22nd July #HappyBirthdayPrinceGeorge.”

People magazine reported the image was captured during a recent trip to the Sensational Butterflies exhibit at London’s Natural History Museum by John Stillwell, a photographer with the British Press Association.

“He’s quick on his feet,” Stillwell told People of Prince George's photo shoot, which was reportedly attended by only a few members of William's and Kate's staff. “He was walking towards me. I was kneeling down to take the picture and he was on top of me as soon as he started walking. He was very quick. He looked really steady on his feet,” he said.

Stillwell said being able to photograph the presumed future king of England was a glorious occasion.

“[I was] really honored to be asked to do it,” he told the magazine.

While the royal family’s museum visit earlier this month was strictly a work-related venture, a spokeswoman for the museum reports the royals said they would visit again in the near future.

“That was a business-focused morning,” said a rep of Prince William's and Kate’s July 2 outing. “But they wanted to come back and have some family time here. … It’s a tropical oasis in the center of London.”

A spokesman for the palace confirmed to People Saturday the anniversary of the young heir’s birth will be celebrated privately with family and close friends inside Kensington Palace Tuesday. Britain’s Queen Elizabeth, the tot's great-grandmother, and Prince Harry, his uncle, are scheduled to attend the affair. Prince Charles and his wife, Duchess Camilla, will not be making an appearance due to work obligations.