The monarch's cancer battle prompts the introduction of a "superfood" lunch by King Charles.

King Charles III has started eating a "superfood" after years of skipping lunch.

The Mail on Sunday reported that the monarch, who is battling an undisclosed form of cancer, now consumes half an avocado with "some reluctance" to keep his strength up. The 75-year-old is known to rarely stop for a midday meal unless a royal engagement or official event requires it.

The king, on the advice of his wife, Queen Camilla, palace aides, and doctors, stopped his habit of skipping lunch.

Charles likes to eat avocados on their own, rather than smashed on toast.

According to Christopher Andersen, author of "The King," the monarch's doctors, including Charles himself, are proponents of holistic medicine and would approve of adding avocado to the king's diet.

"Andersen shared that Charles never ate lunch because he wanted to go to sleep immediately after, so he skipped it. However, he made up for it with large breakfasts, teatimes, and dinners."

Charles is known to prefer a brisk walk over lunch, as he previously told the BBC that he abstains from meat and fish two days a week and excludes dairy on one of those days.

Andersen, who spoke with multiple palace insiders for his book, observed that the king's meals are always prepared to meet his exacting standards.

And there is zero room for errors, he claimed.

"Charles' breakfast tray always had a cup and saucer to the right with a silver spoon pointing outward at five o'clock, as Andersen explained. Butter must come in three balls, not pats, but properly chilled, or they are sent back."

The king's meals are crucial to present well, as Andersen emphasized.

"Andersen stated that the royal toast is always kept on a silver rack and never on a plate. Assorted jam, jellies, marmalades, and honey are served on a separate silver tray. The king prefers round ice cubes in his drinks because he believes squared cubes are too noisy. Breakfast consists of small portions of cereal and cut fruit. According to the servant, Charles dislikes large portions and becomes upset when served in the U.S., where large portions are the norm."

Andersen stated that Charles has a guilty pleasure of indulging in a "highly caloric fruitcake from Wales."

"Butter must come in three balls – not pats of butter, but they must be balls of butter, and they must be three in number. They must also be properly chilled, or they are sent back." — Christopher Andersen, author of "The King"

Dinner is always a big affair, even if the king chooses to skip lunch.

"Andersen stated that the game he shot at one of the royal estates often consists of a green salad with a soft-boiled egg. The egg must be cooked to meet the king's standards of softness, and it's never met on the first try. Occasionally, a half-dozen eggs are sacrificed in the process."

The guests at Clarence House, Windsor, Balmoral, Sandringham, and Highgrove were taken aback by the fact that His Majesty always ate a meal that was different from theirs, which was specially prepared for him. The king never used a saltshaker and instead had a small silver bowl of salt with a silver spoon provided to him wherever he dined.

"He remarked, 'My people are so attentive to my needs,' as the bowl was presented to him during a Windsor dinner, adding, 'They never forget my salt.'"

"The butler who fails to prepare His Majesty's dry martini to his liking will face the same consequences. Before his cancer diagnosis, he would typically consume three or more drinks, including a martini before dinner, followed by wine and an after-dinner drink. In contrast, the Queen Mother would consume six or seven drinks in a 24-hour period, which worked for her as she lived to be 101."

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"Andersen stated that, while undergoing cancer treatment, he has significantly reduced his alcohol consumption, but is still permitted the occasional drink. King Charles, known for his eccentricities, has made adding avocado to his diet for health reasons one of the more rational choices he has made in terms of eating habits."

In October, Charles will visit Australia and Samoa, as announced by Buckingham Palace in July. The monarch has been gradually resuming public duties after taking a break following his cancer diagnosis in early February.

Despite the "limited" program in Australia, Charles' decision to embark on a long journey will be viewed as a positive sign of his recovery.

British Vogue received a brief update from food writer Tom Parker Bowles, the king's stepson, about the monarch's health. Bowles stated that the king is receiving "the best treatment," but admitted that cancer is "really a bastard."

"The king is receiving the best treatment, said the 49-year-old. "He's a great man and a tough man, and you've just got to get on with it. Of course, anyone who has someone they love with cancer is going to worry.""

The Associated Press contributed to this report.