The first photograph of Meghan Markle and Prince Harry's daughter Lilibet has been released to mark her first birthday.

The Sussexes invited close friends and family for a "casual, intimate backyard picnic" on Saturday at Frogmore Cottage, a spokesperson for the couple told People.

In the adorable snap, Lili sits in the yard of her family's home wearing a blue dress and a white lace bow in her red hair.

Misan Harriman, a close family friend of the Sussexes who attended the party, took the "candid, spontaneous photograph that the Duke and Duchess are pleased to share today," the spokesperson added.

And baker Claire Ptak from Violet Bakery in East London created a special birthday cake for Lilibet. Ptak also made Harry and Meghan's wedding cake back in 2018.

The couple travelled to the UK with their two children, Archie and Lilibet, for the Queen's Platinum Jubilee celebrations.

The family stayed at their UK home, Frogmore Cottage, just half a mile from Windsor Castle. They returned to California on Sunday.

The trip was Lilibet's first visit to the UK, as she was born in California. Archie was born in the UK in May 2019 but hadn't been back to visit since he was six months old.

Lilibet also got to meet her great-grandmother Queen Elizabeth for the first time during the trip. She is named after the monarch, as Lilibet was the Queen's childhood nickname.

Meghan and Harry's daughter Lilibet turned one over the weekend. Photo / Supplied

The young Sussexes didn't attend any of the Jubilee events, but Meghan and Harry appeared at the Trooping the Colour and a thanksgiving service in honour of the Queen at St Paul's Cathedral.

They did not attend the Platinum Party at the Palace on Saturday night or the Platinum Jubilee Pageant outside Buckingham Palace.

Several of the royals marked Lilibet's birthday on social media, with the Queen, Prince William and Kate Middleton and Prince Charles and Camilla sharing their birthday tributes.