Prince William has spoken publicly for the first time following King Charles III’s cancer diagnosis.

On Monday Buckingham Palace announced the British monarch had been diagnosed with cancer and would be receiving treatment.

His son William, the Prince of Wales, attended a charity gala for the London Air Ambulance Service on Wednesday evening and thanked well-wishers for their support following the news.

"We really appreciate everyone's kind messages, thank you," Prince William said when he was asked about his father.

The 41-year-old royal waved to fans gathered outside the venue in central London as he arrived at the black-tie event, which was also attended by Hollywood legend Tom Cruise.

As William took to the stage to deliver a speech at the event, he elaborated on recent events.

"Good evening," he told the crowd. "I'd like to take this opportunity to say thank you, also, for the kind messages of support for Catherine and for my father, especially in recent days. It means a great deal to us all."

He even made a joke about the royal family's situation, adding, "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 charity gala was Prince William's second royal engagement of the day, after he also hosted an investiture ceremony at Windsor Castle.

This marked William's return to royal duties after he took time out to care for his wife, Catherine, Princess of Wales, who recently spent time in hospital following her planned abdominal surgery.

King Charles has also publicly spoken for the first time since his cancer diagnosis was revealed.

On Wednesday evening the 75-year-old royal paid tribute to Grenada as he marked the Caribbean country’s 50th anniversary of independence.

"My wife and I hold such special memories of our visit to your beautiful 'Spice Island' five years ago, and of the warm and touching welcome you extended to us,” King Charles said in a statement.

"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! My thoughts are with everyone across Grenada.

"My family join me in sending our heartfelt congratulations to you all."

Meanwhile, the King’s youngest son Prince Harry has flown back to California just 26 hours after arriving in the UK to see his father following his cancer diagnosis.

The Duke of Sussex was seen at London’s Heathrow Airport on Wednesday afternoon after visiting his father on Tuesday.

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