Prince William is now the same age as Princess Diana when she died

The public may still view him as Princess Dianas little boy, but Prince William is now 36 years old — the same age as his mother when she died in 1997.

The duke, who was just 15 when Diana was killed in a car accident in Paris nearly 21 years ago, marked his 36th birthday on June 21. The royal family paid special tribute to the occasion on social media.

The father of three spent part of his special day on official royal duty. According to Kensington Palace, he attended a ceremony honoring a rehab facility for injured members of the Armed Forces, where he read a poem about the death of a soldier and father.

It may have been a somber moment for the royal, given the significance of this birthday. People who have lost parents can experience feelings of anxiety and grief as they approach the age at which their loved one died.

Prince William and Princess Diana in 1991. (Photo: Terry Fincher/Princess Diana Archive/Getty Images)

Both Prince William and younger brother Harry, who are active in promoting mental health awareness, have been vocal in recent years about the grief they felt after their mother died.

“I was in a state of shock for many years,” Prince William told British GQ last year. “People might find that weird, or think of shock as something that is there, it hits you, then in an hour or two, maybe a day or two, you are over it. Not when it is this big a deal; when you lose something so significant in your life, so central, I think the shock lasts for many years.

Prince William spent his birthday in Leeds, England. (Photo: Oli Scarff—WPA Pool/Getty Images)

“I am in a better place about it than I have been for a long time, where I can talk about her more openly, talk about her more honestly, and I can remember her better, and publicly talk about her better,” he added. “It has taken me almost 20 years to get to that stage. I still find it difficult now because at the time it was so raw. And also it is not like most people’s grief, because everyone else knows about it, everyone knows the story, everyone knows her. It is a different situation for most people who lose someone they love; it can be hidden away or they can choose if they want to share their story. I don’t have that choice really. Everyone has seen it all.”

Beyond the Princess Diana connection, 36 is also a significant birthday at the moment, since both Prince William’s wife, Kate Middleton, and his sister-in-law, Meghan Markle, are also that age.

Read more from Yahoo Lifestyle:

Follow us on Instagram, Facebook, and Twitter for nonstop inspiration delivered fresh to your feed, every day.