The Prince of Wales has pulled out of attending a memorial service for the late King Constantine of Greece at Windsor Castle due to a personal matter.

Kensington Palace would not elaborate further but said the Princess of Wales, who is recovering from abdominal surgery, continues to be doing well.

William, who was due to deliver a reading, called the Greek royal family who are attending the service in St George’s Chapel to let them know he was unable to attend.

Constantine II of Greece, who died in January last year, was William’s godfather.

Kate is away from official royal engagements until after Easter following major surgery in January.

The King is also missing the service as he continues treatment for an undisclosed form of cancer.

Charles, who has been staying at Windsor Castle, is due to leave the Berkshire residence at some point on Tuesday morning.

Dozens of foreign royals travelled to Windsor to attend the service but the King is not expected to meet them privately.

Constantine’s eldest son Crown Prince Pavlos is to step in to give the reading in William’s place.

The Duke of York led family members including his ex-wife Sarah, Duchess of York, Princess Beatrice, the Princess Royal and Zara and Mike Tindall, who arrived at the chapel after being driven to the castle quadrangle by coach.

The final member of the British royal family to arrive was the Queen, who was driven down from the castle to the 15th century chapel.

She was warmly greeted by the Dean of Windsor, the Right Rev Christopher Cocksworth, at the Galilee Porch.

The King was close to his second cousin Constantine, who was a first cousin once removed and sailing partner of the late Duke of Edinburgh.

Constantine died at the age of 82 in January last year, decades after being toppled from the throne in a military coup.