William informed the Greek side of the family in a phone call early Tuesday.

The prince has been performing public duties and engagements on his father’s behalf since his cancer diagnosis after being from royal duties for almost a month himself, supporting his wife, Kate, princess of Wales, who is recovering from major abdominal surgery in January.

Kensington Palace, the Wales’ official residence, was quick to quash any suggestion her condition may have taken a turn for the worse, issuing a statement saying her recovery at home progressing as expected and that she was “doing well.”

The memorial service in St. George’s Chapel, where the late Queen Elizabeth II is interred, is to honor the last king of Greece, a second cousin of Charles and a close friend.

Thousands turned out for his Jan. 16 funeral in Athens’ Metropolitan Cathedral where his widow, Anna-Maria, son, former Crown Prince Pavlos, sister, Spain’s former Queen Sofia, sister-in-law Queen Margrethe II of Denmark and Princess Anne were the chief mourners.

Constantine was deposed in a military coup in 1967 leading to a brutal six-year military dictatorship until a people’s revolt leading to the establishment of a republic forced him into a four-decade-long exile in London.

The Greek government banned him and his family from entering the country unless he renounced all rights to the throne due to his refusal to formally recognize the 1974 referendum that abolished the monarchy.

After a series of tentative visits beginning in 1993, Constantine eventually moved back to Greece in 2013 where he lived in Porto Cheli in the Peloponnese before moving to Athens in 2023 where he died at the age of 82.