The King evicted the Duke and Duchess from the property at the beginning of the year, just days after the publication of Harry’s memoir, Spare.
The couple were given until early summer to vacate but are not thought to be planning to return to the UK in the coming weeks.
The Duke flew from Los Angeles to London overnight on Sunday after spending the day celebrating his daughter Princess Lilibet’s second birthday with his family.
It meant he failed to attend the opening day of his claim against MGN in court, earning a rebuke from the judge.
Justice Timothy Fancourt said he was “a little surprised” that his directions had not been followed after instructing the Prince’s legal team that the first witness should have been available on Monday.
In the event, Prince Harry finally appeared on Tuesday and returned to court on Wednesday, undergoing a gruelling eight hours of cross-examination in total which he admitted had been “a lot”.
The Duke left the court shortly after 5pm on Wednesday, waving to onlookers as he was driven away in a black Range Rover.
He is understood to have boarded a flight back home on Thursday afternoon, keen to get back to his family “as quickly as possible”.
The Duke made a similar dash back home after the Coronation last month, when he headed straight to the airport from Westminster Abbey, via a quick vehicle change, having spent just 28 hours in the country.
On that occasion, he was determined to kiss his son, Prince Archie, goodnight on his fourth birthday, which happened to fall on the same day.
In March, the Duke made an unannounced appearance at the High Court to throw his weight behind a legal claim against the publisher of the Daily Mail over alleged unlawful information gathering.
On that occasion, the King was said to have been too busy to see his son.
This week, Charles returned from a private visit to Romania on Tuesday but again did not take the opportunity to see the Duke. Instead, he attended a concert organised by Wigmore Hall at St James’s Roman Catholic Church, in Marylebone, that evening.
On Wednesday, as his younger son returned to the witness box - the first senior royal to do so in more than 130 years - His Majesty presented honours at Buckingham Palace to members of the Army who were involved in Queen Elizabeth II’s funeral.
He later met Ben Wallace, the Defence Secretary, and First Sea Lord Admiral Sir Benjamin Key.
The Duke made no attempt to see his brother, the Prince of Wales, with whom relations are at rock bottom following the litany of personal revelations made in his memoir and various interviews.
