Prince William has pulled out of a memorial service for his late godfather, King Constantine of Greece, because of an unspecified “personal matter”, his office says.

William was due to deliver a reading at the event at Windsor Castle however he cancelled at the last minute, raising speculation and concern among royal watchers.

“Unfortunately, the Prince of Wales is no longer able to attend the King Constantine Memorial Service this morning due to a personal matter,” Kensington Palace said on Tuesday (local time).

William called the Greek royal family to let them know he was unable to attend the service at St George’s Chapel which is walking distance from his home where he is caring for his wife Kate.

The palace declined to give any further details but it comes after Kate, 42, underwent abdominal surgery in January which will keep her out of the public eye for months.

However Kensington Palace released a statement saying the Princess of Wales was “doing well”.

Tweet from @RoyalFamilyITNP

Officials have previously said Kate was making good progress in her recovery and following the announcement on Tuesday, a royal source also confirmed she was continuing to do well.

It is rare, but not unheard of, for the British royals to pull out of an engagement.

Following Kate’s operation, William, the 41-year-old heir to the throne, postponed official duties to care for their three children before resuming engagements earlier in February.

His wife is not due to return to public events until after Easter.

His absence comes as his father King Charles, 75, is also unable to perform his public role as he undergoes treatment for an unspecified form of cancer.

Another royal source said there was no connection between William’s personal matter and the King’s health.

In Charles’ absence, his wife Camilla has become the most senior royal performing engagements.

She was joined by other senior royals at the service at Windsor Castle for the late King Constantine II, who was a relation of William’s grandfather, Prince Philip.

He died aged 82 in January 2023, decades after being toppled from the throne in a military coup.

-with AAP