King Charles did not send Princess Beatrice's daughter a public birthday message amid feud with Prince Andrew

In contrast, when Beatrice's cousin, Prince Harry, celebrated his 40th birthday last weekend, King Charles, Prince William and Princess Kate all sent him public messages on social media.

It comes as Sienna's grandfather, the Duke of York, is currently locked in a royal feud with King Charles.

A new programme titled A Very Royal Scandal dropped on Amazon Prime on Thursday, dramatising Andrew's career-ending Newsnight interview from 2019.

King Charles is likely unhappy about the negative commentary surrounding the Royal Family amid the show's publicity.

Andrew and Charles are also locked in crunch talks over the duke's home, Royal Lodge.

Despite living in his home since 2003, King Charles is understood to want his younger brother to move into a smaller and less expensive property, that is less of a burden on the taxpayer.

One of the reasons the King did not publicly acknowledge Sienna's birthday may be linked to Princess Beatrice and Edoardo Mapelli Mozzi's desire to keep their youngster out of the spotlight.

The princess, 36, generally keeps a low profile on social media and rarely shares pictures of her daughter.

Prince Harry was publicly wished a happy birthday by both Buckingham Palace and Kensington Palace on September 15, after much speculation among royal fans and experts.

It was the first time in two years Buckingham Palace mentioned the Duke of Sussex's birthday in its posts.

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The reason for this is believed to be linked to a decision made by the late Queen Elizabeth II to only publicly mark the birthdays of non-working royals when these end in a zero.

This is also likely another likely reason why Beatrice's daughter did not receive a public birthday message.

The estranged duke is thought to have celebrated his milestone birthday privately with family and friends on Sunday before going on a trip with his closest pals to the Californian mountains.

Just a day before his birthday, Harry joined his wife at a charity tennis tournament in LA.