The Duke and Duchess of Sussex are currently living in Los Angeles after stepping down as senior royals and are set to mark their son's first 12 months at their home.
A post on the official Royal Family's Instagram account read: "Happy Birthday to Archie Mountbatten-Windsor who is celebrating his 1st birthday today! ... Archie is The Queen's eighth great-grandchild."
Kensington Palace, the home of the Duke and the Duchess of Cambridge, also took to Twitter to wish Archie a happy birthday by sharing a family portrait.
Alongside a red balloon emoji, they wrote: "Wishing Archie a very happy first birthday today!"
Clarence House shared a photo of Prince Charles with his son Prince Harry and grandson Archie.
They wrote alongside it: "A very Happy Birthday to Archie, who turns one today. This photo of Archie and his grandfather was taken following his christening in July 2019."
It comes after royal expert Katie Nicholl revealed that the couple plan to video call with their family in the UK to celebrate Archie's milestone birthday.
She said: "The Queen will wish him happy birthday this week via Zoom as will the Cambridge children. They haven't seen their little cousin in months so they've been looking forward to seeing how much he's grown."
The couple are expected to ask anyone wanting to send a present to instead make a charity donation as Archie "has everything he needs".
Meanwhile, Archie is "desperate" to talk, "is well on his way to walking" and is a "very confident little boy".
Royal expert Nicholl said: "I spoke to someone who had been sent a video of Archie a few weeks back. He said that he is super cute and a really, really happy little boy.
"He's burbling and sort of desperate to talk, but certainly already mastered cruising and is well on his way to walking. He may even be walking already. I was told very cute, very, very happy, and very confident little boy."
