King Charles III Attends Easter Service Amid Cancer Battle

King Charles III may be ill, but he bounced back for a big public appearance Sunday ... attending Easter services at Windsor Castle.

KC and Camilla rolled up to St. George's Chapel and there was fanfare waiting for them. The clergy met them outside as Charles waved to onlookers.

There were differences this year because of Charles' medical treatment ... he's undergoing chemo for cancer, which compromises his immune system, so he and Camilla were seated apart from the rest of the royals. He also skipped the reception after the service.

There were other royals present, including Prince Andrew and his live-in ex-wife, Sarah Ferguson. Princess Anne was also there, along with Prince Edward.

Prince William and Kate Middleton, along with their kids, were absent. As you know, she's also battling cancer and is undergoing treatment.