The young royal no doubt marked the milestone occasion at home in Montecito with her doting parents and her older brother, Prince Archie, four. The family relocated to California in March 2020, just months after stepping down as senior working royals.
And whilst it's become somewhat traditional for key members of the British royal family to share their birthday messages online, senior royals did not publicly wish Princess Lilibet Diana a happy birthday.
There is a valid explanation, however… HELLO!'s Online Royal Correspondent Danielle Stacey explains: "In recent years and certainly since King Charles III's reign began in September 2022, we have only seen public messages from the royal family's social media accounts for working members of the royal family, such as the Prince and Princess of Wales and their children, the Duke and Duchess of Edinburgh and the Princess Royal.
"The Duke and Duchess of Sussex stepped back as senior royals in 2020, and no longer carry out royal duties. Similarly, the palace doesn't typically share messages on the likes of Princess Beatrice, Princess Eugenie and Zara Tindall's birthdays nor their children's special days."
Princess Lilibet's birthday celebrations coincided with Prince Harry's return to the UK. The royal is due to make a court appearance on Tuesday as his case against Mirror Group Newspapers rumbles on.
The case has been brought against Mirror Group Newspapers (MGN) by the Prince and other high-profile figures over alleged unlawful information gathering, including phone hacking. Harry is one of four representative claimants whose cases have been selected for trial.
This isn't the first time the Duke of Sussex has been forced to interrupt key family celebrations in recent months. On 6 May, the royal took a commercial flight from California to London in order to support his father King Charles III at his historic coronation.
Given that 6 May also marked his son Prince Archie's fourth birthday, Prince Harry made a swift exit shortly after the service at Westminster Abbey.
It has since been revealed that Harry caught a British Airways flight that arrived at LAX airport at 7.30pm local time (3.30am UK time), allowing him to get home to Montecito in time to see Archie on his special day.
Despite only being in the UK for a brief spell, Harry appeared to enjoy his time on British soil, chatting animatedly with his cousins, as well as his aunt, Princess Anne.
For the special occasion, Prince Harry donned a smart morning suit adorned with his military medals.
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