The official Twitter account of the Duke and Duchess of Cambridge posted a message, writing "Wishing a happy 40th birthday to The Duchess of Sussex!" alongside a picture of Meghan and a birthday cake emoji.

The Queen's official account posted three pictures to mark the occasion, including a photo of Meghan, the Duke of Sussex and their son Archie on their 2019 royal tour to South Africa.

Another of the photos shows the monarch with Meghan in Cheshire in 2018 for their first joint royal engagement, while the third is of a smiling Meghan and Harry at the Endeavour Fund Awards last year.

The post said: "Wishing The Duchess of Sussex a very Happy Birthday today!"

The Clarence House account for the Prince of Wales and the Duchess of Cornwall also tweeted a picture of Meghan smiling, writing: "Wishing The Duchess of Sussex a very happy 40th birthday."

Meghan and Harry are likely to have planned a low-key celebration as they are reportedly taking time off to care for the latest addition to their family, baby Lilibet - known as Lili - who was born exactly two months ago on June 4.

Lili's birth came after the duchess experienced the heartbreak of a miscarriage a few weeks before her 39th birthday.

The Sussexes have established a new life for themselves in the celebrity enclave of Montecito in California, buying a multimillion-pound home and launching a non-profit foundation.

Harry and Meghan have also signed lucrative deals with Spotify and Netflix that have given them the capital to pursue their new lifestyle and public goals.

Much has been written about their decision to step down as senior royals for personal and financial freedom early last year, which was dubbed 'Megxit'.

But it was only when the couple sat down for their much-anticipated television interview with Oprah Winfrey in March that they told the world their side of the story.

Meghan and Harry laid bare their brief lives as a working royal couple, alleging a member of the family - not the Queen or Philip - made a racist comment about their son, and how the duchess had suicidal thoughts but her approaches to the monarchy for help were turned down.

Winfrey was left opened mouthed when the duchess - the first mixed-race member of the modern monarchy - said a fellow royal was worried about how dark their son Archie's skin tone might be before he was born.

Buckingham Palace later said the Queen was "saddened" to hear about Harry and Meghan's struggles but added "some recollections may vary" over the other allegations.

Harry is to write his own tell-all memoir and has promised to write an "accurate and wholly truthful" account of his life.

Australian Associated Press