Meghan Markle and Prince Harry send private letter to British business following Prince Archie's birthday

The red bike was hand-delivered to the Sussexes' Montecito home by Martin Watson, co-owner of Mad Dogs & Englishmen, a bike shop in the US town.

Watson did not hear anything regarding his delivery until this week when he received a letter.

It said: "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."

The letter was signed by Harrison Colcord, who is thought to have recently been hired by the Duke and Duchess of Sussex.

Jennifer Blevins, Watson’s partner, provided an insight into the decision to gift Prince Archie a birthday present.

She told People: "He went and got one of our little Specialised bikes – they’re really nice little bikes – and he’s like, 'This one’s perfect. It’s got training wheels,'"

"So he went and got some birthday balloons, and he got some flowers for Meghan and a birthday card, and he said, 'OK, I’m gonna bike over and take it to their house.'"

Watson was greeted by the Sussexes' security upon arrival, who asked if he had received an invitation from the couple.

After running an on-site background check, they allowed him to leave the flowers, card, balloons and bike.

The next day, Watson and Blevins posted a picture of the bike on their company’s Instagram.

They captioned the post: "We hope yesterday’s special birthday boy had a wonderful day, surrounded by lots of love, friends and family.

"Martin gifted him a new kid’s bike out of our Montecito shop. We really hope he enjoys it. His little sis can ride as well when she gets a bit bigger."