Harry and Meghan release new photo of baby Archie

Harry and Meghan have released an adorable photo to celebrate Prince Charles' birthday. Photo / Instagram / Chris Allerton

Prince Harry and Meghan have released a sweet new picture of Prince Charles and baby Archie to mark the Prince of Wales' birthday.

The photo was posted to nearly 10 million followers of their combined The Duke and Duchess of Sussex Instagram account on Thursday morning UK time.

It shows Prince Harry holding Archie during his Christening in July as his grandfather looks on. "Happy birthday to His Royal Highness The Prince of Wales — Sir, Pa, Grandpa!" the caption said.

Prince Charles has turned 71 and is currently the longest-serving heir apparent in British history.

The controversial couple have been fiercely protective of their newborn, with Archie only being seen publicly a handful of times in recent months, including on their recent trip to South Africa.

The Duke and Duchess of Cambridge and the Queen and Prince Philip also posted their own tributes to Prince Charles.

The release of the picture came after it was revealed the Sussexes would not spend this Christmas — Archie's first — with The Queen, breaking with long-held tradition.

View this post on Instagram

Happy birthday to His Royal Highness The Prince of Wales - Sir, Pa, Grandpa! 🎂 Photo credit: Chris Allerton © SussexRoyal

A post shared by The Duke and Duchess of Sussex (@sussexroyal) on Nov 14, 2019 at 1:22am PST

It was thought they would spend thanksgiving in the US with Meghan's mum Doria Ragland, 63, and return for Christmas at Sandringham.

But they informed Her Majesty, 93, they will not be joining her and Prince Philip, 98.

Harry has always spent Christmas at the Queen's Norfolk home, except for 2012 when he was in Afghanistan — and for the past two years he has been joined by Meghan, 38.

Harry and Meghan are separating themselves from William and Kate over the holiday season. Photo / Getty Images

"They need some time away to recharge and decide their plans for next year," a royal source told The Sun.

Royal biographer Ingrid Seward said Her Majesty "might be a little hurt but she's far too gracious to ever let it show or be known".

Wishing a very happy birthday to The Prince of Wales!#HappyBirthdayHRH 🎂 pic.twitter.com/TGpiL7a1ro

— The Duke and Duchess of Cambridge (@KensingtonRoyal) November 14, 2019