King Charles’ health condition is progressively deteriorating, leading Buckingham Palace officials to keep a regularly updated plan for his impending funeral — preparations for which started the day after Queen Elizabeth was buried, insiders said.

The 75-year-old monarch has remained largely out of the limelight since announcing his cancer prognosis in February to hide his declining condition, with multiple sources telling The Daily Beast the situation is “not good”.

“Of course he is determined to beat it and they are throwing everything at it. Everyone is staying optimistic, but he is really very unwell. More than they are letting on,” a source described as an old friend of the royal family told the outlet.

King Charles has never revealed what cancer he has been diagnosed with but admitted that it wasn’t prostate cancer, which is one of the most treatable forms of the disease.

Behind the scenes, however, King Charles’ aides are regularly reviewing copies of a several-hundred-page document outlining his royal funeral plans, dubbed “Operation Menai Bridge.”

“The plans have been dusted off and are actively being kept up to date. It’s no more than what you would expect given the king has been diagnosed with cancer. But the circulation of them has certainly focused minds,” a former staffer with links to the serving courtiers told the Daily Beast.

The extremely detailed document was created the day after Queen Elizabeth was buried on September 8, 2022 — and uses the longest-serving queen’s funeral as a field guide on to ensure Charles’ runs more smoothly.

Military officials confirmed to the Daily Beast that Operation Menai Bridge is being regularly updated, but emphasised it was standard procedure and that “it would be “absurd to read anything into” that fact.

All royal members of the plan have updated funeral plans that are categorised by bridge-based codewords.

“Of course they are looking at every aspect of Menai Bridge. The queen’s funeral went like clockwork and set a high bar. It’s not an emotional thing, it’s a job, one taken very seriously, and understandably no one plans to get caught out,” said a senior official involved in the planning of royal funerals.