London, UK - Despite a challenging battle with cancer, Kate Middleton is reportedly preparing to take on her role as Britain's future Queen "sooner than expected".

Just last week, the 42-year-old attended a church service and made a rare comment about her cancer.

The event marked her largest public appearance since she revealed her diagnosis in March this year.

But Princess Kate is not the only one battling the serious illness – King Charles (76) has also been affected by cancer.

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As People reported on Wednesday, his wife Camilla (77) has also been struggling with health problems, including a recent bout of pneumonia.

In light of the royal couple's serious health restrictions, they both had to cut down their commitments significantly, putting the onus on Kate and William.

Behind the scenes, however, plans are reportedly already being prepared for the succession of Camilla and Charles, with Kate and William next in line.

"There's a sense of calm before the storm," a royal expert told People.

"They are next in line for the biggest job of their lives, and of course, Kate's health has taken priority, but it's also allowed everyone to take a step back and figure out what’s important right now."

The Prince of Wales is "taking on more responsibilities" amid his father and step-mother's health challenges, while both he and his wife are preparing for their respective roles as King and Queen "sooner than they would have expected."

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William recently attended the re-opening of the Notre Dame cathedral, where he mingled with several world leaders, including Donald Trump.

The US president-elect shed some rare light on the health battles within the British royal family, saying of William, "I asked him about his wife, and he said she's doing well. And I asked him about his father, and his father is fighting very hard, and he loves his father, and he loves his wife, so it was sad."