Prince William has thanked the public for their well wishes following his father King Charles III's shock cancer diagnosis, as the monarch made his first statement.
Charles sent a message to Grenada, celebrating the Caribbean island marking 50 years of independence.
While the message mostly focused on the nation and the king's memories of visiting, he did note at the end he was not able to celebrate in person.
"I can only say how sorry I am that I cannot be with you in person to mark this momentous milestone, and to enjoy a little Oil Down with you all!" the king wrote.
"My thoughts are with everyone across Grenada, Carriacou and Petit Martinique, and all those in the Grenadia."
Meanwhile, William took centre stage of royal public duties as his brother Prince Harry was set to return to the United States without speaking to his brother.
"I'd like to take this opportunity to say thank you … for the kind messages of support for Catherine and for my father, especially in recent days. It means a great deal to us all," the Duke of Cambridge said at a gala dinner for London's Air Ambulance Charity.
"It's fair to say the past few weeks have had a rather 'medical' focus.
"So I thought I'd come to an air ambulance function to get away from it all."
The event was the royal's second official public appearance on Wednesday (local time) after returning to work following his wife Kate's planned abdominal surgery on January 16.
The Princess of Wales spent two weeks in hospital recovering.
Since then, Buckingham Palace announced on Monday that tests on Charles revealed the 75-year-old had a form of cancer.
With the king postponing public duties to undergo out-patient treatment and Kate not expected to return to engagements until after Easter, the onus will be on remaining royals, especially William and Queen Camilla, to be the monarchy's public face.
Royal author Robert Hardman said William had already taken on substantial state duties towards the end of Queen Elizabeth's reign when she was hampered by mobility issues.
"In that regard, it's not that different but obviously there's the burden of expectation," Mr Hardman told Reuters.
"On many occasions he will have to stand in, he'll be sort of quasi head of state in much the same way that Prince Charles was when the queen was infirm."
On Tuesday, the king travelled with Camilla to Sandringham House, his home in eastern England, after a 30-minute meeting with son Harry.
Harry has barely been on speaking terms with many of the Windsors following his criticism of the monarchy since stepping down from royal duties almost four years ago.
A royal source said there were no plans for him to see his elder brother William during his visit to Britain.
After only about 24 hours in Britain, Harry returned home to California without seeing his brother.
The king is due to speak with Prime Minister Rishi Sunak by phone on Wednesday, Mr Sunak's spokesman said.
Buckingham Palace has not given any details of the king's condition, other than to say it was not prostate cancer, but said he was remaining "wholly positive" and looking forward to returning to public duty as soon as possible.