London, UK - Following the dual cancer diagnoses of King Charles and Kate Middleton, the British royal family are facing a difficult Easter this year.

Britain's King Charles III attended an Easter church service on Sunday, in his most high-profile public appearance since revealing a cancer diagnosis earlier this year.

Charles and his wife, Queen Camilla, arrived by car for the hour-long late morning service at St George's Chapel within the grounds of Windsor Castle, west of London.

The 75-year-old, dressed in a suit and light blue tie, smiled and waved to crowds – who had queued up for hours for a glimpse of the ailing monarch – before he entered the chapel.

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Leaving the service, Charles and Camilla greeted some of the well-wishers lined up outside, shaking hands and briefly chatting to some in the crowds.

Attending the annual religious ceremony is a long-standing annual tradition for the royals, with other family members in attendance on Sunday.

But heir-to-the-throne Prince William and his wife Catherine were notable absentees this year, as the 42-year-old Princess of Wales receives treatment following her own cancer diagnosis which was revealed just last week.

According to a report in the British Mirror, the Princess of Wales, her husband, and their three children – Prince George (10), Princess Charlotte (8), and Prince Louis (5) – will stay away from church this year and spend the holidays with their family.

"They want to go away for Easter, spend time together, all five of them, and shut themselves off from the world," an insider told the newspaper.

The mother-of-three made her illness public on March 22. She is now receiving preventative chemotherapy.

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After her abdominal operation in January, Kate originally wanted to make her first public appearance at Easter.

Since the cancer was detected, however, her return to the limelight will be delayed indefinitely.

Regardless of the notable absence, the royal family wished the world a happy Easter via social media for the occasion.

Earlier this week, King Charles also released a pre-recorded Easter audio message – broadcast in his absence at a Maundy Thursday service in Worcester Cathedral, central England – stressing the importance of acts of friendship.