Prince Harry and Meghan Markle's oldest child Prince Archie turned four last month. Photo / Twitter

Prince Archie got a very special delivery for his fourth birthday.

Prince Harry and Meghan Markle’s oldest child celebrated his fourth birthday on May 6 while his father was in the UK for King Charles’ coronation, with ‘low-key’ celebrations planned for when Harry returned home to California.

And this year for his birthday, Archie got a surprise gift from a local bike shop.

The owners of Mad Dogs + Englishmen Bike Shop in Montecito, Jennifer and Martin Blevins, chose a bike for Archie and hand delivered it to the Sussexes’ home, as well as some flowers for his mum Meghan.

Speaking to People magazine, Jennifer said that Martin chose one of the shop’s specialised kids’ bikes for Archie, saying, “This one’s perfect, it’s got training wheels”.

“And so he went and got some birthday balloons, and he got some flowers for Meghan and a birthday card, and he said, ‘Okay, I’m gonna bike over and take it to their house.’”

When Martin arrived, security asked him if he’d been invited by the Sussexes, and he replied, “I’m just a British business in town that wanted to give Archie a gift”, according to Jennifer.

After security checks, he was permitted to leave the gifts and card. And this week, the store owners received a surprise delivery of their own - a thank you letter from the Duke and Duchess of Sussex.

“A courier came by our little shop on Coast Village Road and he dropped off that letter,” Jennifer told the outlet.

“I was making a joke, I said, ‘It better be a thank you letter,’ and it really was! I wasn’t expecting that. I had no idea.

“It was so thoughtful because, you know, they took the time to write something personal and not just a generic thank you.”

The letter was signed by Harrison Colcord from the Sussexes’ office, and read, “On behalf of Prince Harry and Meghan, The Duke and Duchess of Sussex, please accept their sincere thanks for the thoughtful gift you sent to Prince Archie for his fourth birthday.

“The bike has brought much joy, and is most appreciated by the family. They asked that I convey their gratitude at the lovely surprise.”

Jennifer said she and Martin were shocked to receive the letter, saying, “Every celebrity in that town has bought bikes from us, and they all come through there.

“None of them ever sent a thank you letter.”