Prince Philip participated in a special royal engagement Wednesday, July 22, and during this rare public appearance since his retirement in 2017, the Duke of Edinburgh showed that he's still energetic, robust and healthy at 99 years old. 

Body language expert Judi James told Daily Express that Prince Philip was beaming as he came out of the doors of Windsor Castle for his first formal royal engagement in quite a long time. Queen Elizabeth's husband stood upright as the ceremony to hand over his military role in The Rifles to Camilla, the Duchess of Cornwall, was underway.

The royal's appearance apparently indicated to the world that he's back and still able to take on his duties. James, however, said that Prince Philip appeared to have an unsteady gait when he started walking. He also looked like he was struggling to talk to the guards, suggesting a loss of hearing. 

The body language expert said that while these are indicators of the royal's aging process, Prince Philip generally still looks robust and healthy. At 99 years old, he stood up like he had the bearing of a much younger man.  

James said that Prince Philip had a "twinkle in his eye," as if he knew that the world would be astounded at his latest public appearance. The Duke of Edinburgh drew worries a few months back after Buckingham Palace confirmed that he stayed at a hospital for four days after a routine procedure for a pre-existing condition. 

There are also worries over Prince Philip's health because, like Queen Elizabeth, he is at an age that's vulnerable to the coronavirus. The Queen and the Duke of Edinburgh have been isolating from the virus, under strict safety protocols, in Windsor Castle since March.

When the Queen turned 94 in April, she and Prince Philip posed for a photo while in isolation to show that they remain in good health. The Duke of Edinburgh also released a rare statement to thank those in the frontlines for their vital and urgent work to help the public during the pandemic. 

According to reports, the prince was moved by how people have been coming together to keep essentials like food, postal services and rubbish collection working despite the lockdown's interruption of daily activities. Prince Philip also hailed healthcare workers, medical and scientific experts, as well as those in research in trying to find a treatment for the virus. 

Prince Philip retired from public life in 2017 at the age of 96. During his entire career, the Duke of Edinburgh was a member, patron or president of over 780 organizations and charities. He has also written over 14 books and joined Queen Elizabeth in thousands of royal trips both in the U.K. and abroad.