Prince William Celebrates 40th Birthday, Prince Charles Leads Tributes

It's a special day for Prince William, and his father -- first in line to the throne -- is leading the charge to honor his oldest son, and future King of England, on hitting the ol' 4-0.

Prince Charles did that typical parent thing ... busting out old pics of himself with Will, from his birth, his adolescence and right up to current day -- and he wrote, "Wishing The Duke of Cambridge a very happy 40th birthday!"

Of course, the current monarch, Queen Elizabeth, also had some words and pics for her grandson ... but it might be the most royally royal birthday message ever.

The pics posted to Her Majesty's Family account are accompanied by said caption ... "Prince William Arthur Philip Louis is the elder son of The Prince of Wales and Diana, Princess of Wales. He was born at 9.03pm on 21 June 1982, at St Mary’s Hospital, Paddington, London."

Ya gotta read it with a British accent.

The IG post included more infant pics and moments the Queen and William have shared together.

Worth noting ... William's bro, Prince Harry, hasn't posted any birthday wishes yet. It's still early on the West Coast, but it'll be interesting to see if he does mention the milestone amid their rift.

Apparently, Prince William and Kate Middleton will reportedly celebrate "in style" with a joint 40th Bday party at Windsor Castle.

Her birthday was back in January but the celebrations were reportedly nixed due to COVID-19.

Interestingly, the Duke's birthday will not be marked this year by the flying of the Union Jack over government buildings. That honor is now reserved for the Queen and Prince Charles' birthdays.