King Charles' comical quirks revealed by royal insider: 'He used to get mocked'

King Charles has never met a tree he didn’t like.

The British monarch and environmentalist shakes hands with every tree he plants to wish it well. That's according to Daily Mail reporter Robert Hardman in his new book, "The Making of a King: King Charles III and the Modern Monarchy." It explores the 75-year-old’s reign and the pivotal events that led to his coronation in May.

"He does love being out and about in the countryside," Hardman told Fox News Digital. "He’s always disappearing, and he’s got a particular thing at the moment with planting trees. He’s obsessed with it. He’s always liked planting trees. He used to get mocked for it slightly because whenever he planted a tree, he’d always shake one of the leaves by the hand and say, ‘Good luck tree.’"

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King Charles III has been planting more trees than ever, royal author Robert Hardman says. (Samir Hussein/WireImage)

"The tree planting has gone up a notch since he became king," Hardman shared. "He is now planting so many trees. I talked to one of his staff, and he said, ‘Well, we often joke, "Where’s the king? He is probably planting trees."' And it turns out … he is planting trees. He’s not at his desk, he’s out in the garden."

When Charles isn’t flexing his green thumb, he maintains a daily exercise regimen developed for the Royal Canadian Air Force, the book says. He’s also an avid skier and has been a regular visitor to the Swiss resorts of Klosters since he took up the sport in 1978. He skips lunch, and when he’s hosting a formal luncheon, guests can expect to see him with an empty plate.

And those who spend time with the king will likely freeze because he prefers keeping his windows wide open, no matter the season, for "fresh air."

Queen Camilla is all too familiar with the king's tree-planting habits. (Hannah McKay/Pool/AFP)

But when it is time to eat, he prefers fish to red meat, as well as his favorite dish.

"Eggs and spinach are his favorite foods," said Hardman. "He loves eating eggs."

According to the book, Charles also enjoys foraging for mushrooms, which he’ll serve to guests at dinner. And he’s known for sharing "coded messages" by using his ties.

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King Charles III poked fun at himself with a dinosaur-print tie. (Max Mumby/Indigo)

"His favorite has a little T-Rex motif on it," said Hardman. "I thought, ‘That’s a bit odd. I keep seeing this tie with a dinosaur on it …' Of course, his cipher says, C. Rex, Charles Rex. So, I think he’s having a little joke about being king with his tie. But he’s in a good place. He’s a happy monarch."

The king’s health recently made headlines. On Monday, Buckingham Palace announced that the royal was released from the hospital after undergoing surgery for an enlarged prostate.

"The King was this afternoon discharged from hospital following planned medical treatment and has rescheduled forthcoming public engagements to allow for a period of private recuperation," the palace said in a statement.

King Charles III leaves with Queen Camilla after receiving treatment for an enlarged prostate at The London Clinic on Jan. 29, 2024. (Chris Jackson)

"He would like to thank the medical team and all those involved in supporting his hospital visit, and is grateful for all the kind messages he has received in recent days," the statement added.

The king was admitted to The London Clinic, the same hospital where his daughter-in-law, Princess Kate, underwent abdominal surgery. His condition was described as benign. It is understood that Charles wanted to share his diagnosis in hopes of encouraging men to get their routine checkups.

Charles left the hospital in London alongside his wife, Queen Camilla.

Robert Hardman's new book, "The Making of a King," is out now. (Pegasus Books)

Hardman said that Camilla is "crucial to everything." 

The pair reportedly first met at a polo match in 1970. They quickly became close, but their romance was interrupted when Charles went on naval duty. They went on to marry different spouses.

In the early ‘90s, Charles’ wife, Princess Diana, went public with her resentment of their relationship. The sensational details that followed caused an embarrassing scandal for the royal family. Camilla and her husband divorced in 1995, shortly after Charles admitted to having an affair with his longtime love. Charles and Diana called it quits the following year. In 1997, Diana was killed in a car crash. Charles waited until 2005 to marry Camilla in a private civil ceremony.

Hardman said Camilla, 76, has been an essential support system for the king.

King Charles and Queen Camilla were crowned on May 6, 2023, in London. (Brandon Bell)

"She lifts the mood around the court," Hardman explained. "He’s always in a happier mood when she’s around. She’s fun. I think she has the right balance of ensuring that things are done properly and that everything is kept on time, but at the same time, bringing a sort of lightness of touch. Because when you get a change of monarch … you get a change of leadership. It means a set of new codes. There’s a new way of doing things. Often people want to know how … the new boss likes to operate, and so everyone’s a little bit worried about doing the wrong thing or getting things wrong."

When it comes to royal engagements, Queen Camilla has a handy trick that involves her purse. (Max Mumby/Indigo)

"She’s the one who could say, ‘Don’t worry, darling. Don’t be so silly. That doesn’t matter,’" Hardman continued. "She’s also the one when things are running over time – he loves talking to people. And if he’s in a crowd chatting, and he meets someone interesting, he’ll just sort of carry on having a conversation. The staff are a bit nervous about going up and dragging him by the arm and saying, ‘Come on, we’ve got to go.’ She could do that."

"And she has quite a good trick," Hardman noted. "She uses the sharp corner of a handbag, and she sticks it on his back. And when he’s going on too long, it’s sort of a signal for ‘Come on, we’re late.’"

"I think we all need the occasional handbag in the small of our backs," Hardman chuckled.

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Robert Hardman says King Charles III likes to forage for mushrooms and serve them to guests at dinner. (Tim Graham Photo Library)

This isn’t the first time Charles’ quirks have been shared in a book.

In 2022, Christopher Andersen wrote a book about the monarch titled "The King: The Life of Charles III." According to Andersen, there are a few surprising things that Charles just can’t leave the palace without.

"He still travels with a childhood teddy bear … he’s had since he was a very small child," Andersen told ETOnline. "The only person who’s been allowed to mend King Charles’ teddy bear is his childhood nanny, Mabel Anderson, who he remains very close to."

Christopher Andersen previously said King Charles III still has his childhood teddy bear. (Chris Jackson/WPA Pool)

Andersen also told the outlet that Charles "travels with a custom-made toilet seat" made fit for a king. Palace insiders have also said that "when he goes to dinner parties at other people’s homes, he often brings his own chef, so they can prepare a meal for him that he’ll eat separately at the table."

"He wants what he wants when he wants it," Andersen added.

That wasn’t the only quirk Andersen discovered along the way.

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Then-Prince Charles is seen enjoying a mojito during a visit to Cuba on March 27, 2019. (Chris Jackson)

"A number of royals have this, the queen had it as well – they don’t like square ice cubes," he said. "They carry around ice cube trays. [They] have them brought with them wherever they go because they don’t like the clinking sound that square cubes make."

Royal photographer Chris Jackson told Fox News Digital ahead of the coronation that the king is known for making an entrance in his vintage Aston Martin, just like James Bond.

"Did you know he had an ejector button in his Aston Martin? Probably not," Jackson told Fox News Digital at the time.

Charles is seen here driving his 1969 Aston Martin DB6 Volante circa 2005 in Cirencester, England. (Max Mumby/Indigo)

"He’s got this beautiful Aston Martin that runs on biofuel, which is basically surplus wine and cheese whey, which is pretty incredible," Jackson said. "He’s obviously very passionate about the environment, [and] he’s got this beautiful car, a DB6 Volante Aston Martin, that’s environmentally friendly."

The king, who has been a longtime advocate of sustainable living, bought the car in 1970. He converted it to run on biofuels, which uses ethanol created from cheese-making whey and wine. He loaned his beloved vehicle to his son, Prince William, who used it to drive Princess Kate for their nuptials in 2011.

Charles’ cousin, Lord Snowdon, once joked, "How does [the former] Prince Charles drive his Aston Martin? Caerphilly."

The Associated Press contributed to this report.

Stephanie Nolasco covers entertainment at Foxnews.com.