REVEALED: King Charles III Plans to Abdicate The Throne to 'Panicked' Prince William: Report

Devastated by a medical crisis, King Charles III is reportedly planning to abdicate his throne in favor of his oldest son and heir, Prince William, after serving less than 18 months as monarch — but it was already in the cards before his cancer diagnosis, RadarOnline.com has learned.

Without divulging details, Buckingham Palace announced on Monday that the monarch, 75, has been diagnosed with cancer.

The 75-year-old's rumored decision has reportedly plunged 41-year-old William into panic, spilled a high-level insider, who also revealed the Prince of Wales doesn't want to be king.

"William is horrified his workaholic father is quitting — it's the last thing he expected," the insider told the Globe last month before his health issues were revealed. "Charles always vowed he would use his mother, Queen Elizabeth II, as an example and rule until his dying day."

"After all, he waited 70 years for the crown. But his rapidly declining health has him starring death in the eye," the insider added.

The well-placed source claimed King Charles has "decided he wants to spend his final days quietly with the love of his life. But William is beside himself; he's not ready and is begging Charles to reconsider."

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Prince William's private life is said to be in shambles. His wife, Princess Kate, 42, just spent two weeks in a hospital after undergoing grueling abdominal surgery for what insiders reportedly claim was ovarian cancer, though the palace officially denies the diagnosis.

"Kate faces a long uphill battle to get back on her feet — and isn't expected back in public before Easter," the insider revealed.

"William is begging his father to remain on the job until nature takes its course. He and Kate want to spend more time raising their three young kids before ascending to the throne."

Meanwhile, royal insiders claimed Charles' rogue son, Prince Harry, was blindsided by the king's decision to step down. Harry was purposefully cut out of the loop — and not informed of the abdication — just like he had to learn about his father's surgery and prolonged hospital stay in American newspaper reports.

Charles' operation at a London hospital came on top of the monarch's battle with a deadly congestive heart failure, an open secret he's attempted to hide for years.

"His declining health has made him realize how short life is and how much he wants to spend it with his darling wife out of the public eye and working in his gardens," another insider dished.

"It will take time to finalize the transfer of power — and he's convinced William will be ready and Kate will make a fantastic queen after a few months of convalescence," the source continued. "Still, William is desperately begging his father for more time, but his pleas are falling on deaf ears."