Book reveals King Charles and Queen Camilla's intense competition over shared 'obsession'.

Over the years, mushroom hunting has brought King Charles and Queen Camilla closer together as a shared hobby.

In his new book, "Cooking & the Crown," Tom Parker Bowles, a British food critic and the monarch's stepson, disclosed that the couple is fiercely competitive about their foraging efforts, particularly when it comes to wild mushrooms, which they both have a deep passion for.

""The silent hunt for wild mushrooms is a popular pastime in many countries, including Italy and Scotland, where the fall season produces the most delectable specimens such as chanterelles, which have a bright yellow color and an apricot-like scent," Parker Bowles told Planet Chronicle Digital."

"Wild mushrooms are somewhat of an obsession, with Charles III and Queen Camilla deeply competitive about their hauls." — Tom Parker Bowles, author of "Cooking & the Crown."

"The 49-year-old shared, "We go looking for mushrooms. The king is a great mycologist, and my mother also loves it. They get competitive, both being very good at it. Of course, they're always taken straight to the kitchen and served with pasta.""

In Parker Bowles' book, it is stated that there is a "5 p.m. ritual" where all palace staff gather around a round table for a meal after an afternoon of mushroom hunting. The book also includes several popular royal recipes that feature mushrooms.

Since Queen Victoria, the royals have utilized the produce from their estates, boasting large kitchen gardens and herds of dairy cows for milk, cream, yogurt, and butter, as stated by Parker Bowles.

"In Edward's time, there were no fridges or strawberries imported from far-off places. People ate what was in season. Of course, the king was an accomplished gardener and mushroom picker. He had a wealth of knowledge about mushrooms and could identify which ones were poisonous."

The king and queen share a passion for their hobby, but differ in their eating habits. According to Parker Bowles, his mother, 77, enjoys porridge in the winter and yogurt in the summer for breakfast. For lunch, she prefers a light chicken consommé or smoked salmon.

The king, who is 75 years old, prefers dried fruit and honey for his morning meal and does not consume 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. Charles is known to rarely stop for a midday meal unless a royal engagement or official event requires it.

WATCH: KING CHARLES, QUEEN CAMILLA ARE COMPETITIVE OVER UNIQUE HOBBY: AUTHOR

The king, on his wife's orders, broke his habit of skipping lunch, as advised by his palace aides and doctors. However, the outlet reported that Charles prefers to eat avocados on their own, rather than smashed on toast.

Parker Bowles stated to Planet Chronicle Digital that since he is currently following the advice of his doctors, it is not for him to provide a comment on the matter.

"He is incredibly disciplined, he said. "The king… knows a huge amount about food… he's championed farmers for many years… He's a great person to talk to about food. He knows a hell of a lot more than I do.""

Charles and Camilla prefer to maintain their eating habits by consuming mushrooms picked from Balmoral and cooking them with pasta, which makes for an ideal dinner.

"The size of breakfast has decreased, lunches are now one course instead of 12, and dinner is at most three courses. However, state banquets have remained constant since Queen Victoria's time. They involve pomp and ceremony, with gold and glassware shining and red-coated footmen. Whether it's President Obama or the emperor of Japan, state banquets are about soft diplomacy, bringing people together through good food."

Tea remains unchanged, with everyone stopping for it at 5 pm. This is a quintessential British tradition, not limited to the royal family. When I visit Scotland for tea, it is typically accompanied by a chocolate cake, fruit cake, scones, clotted cream, and jam.

"Hammond's mustard sandwiches and egg sandwiches are among the offerings, along with potted shrimps and crumpets with Marmite. This is a feast in itself... The tea is still very important."

For afternoon tea, Parker Bowles’ book features a recipe for Welsh teabread, "inspired by King Charles' kitchen." The dish, made with strong Earl Grey tea, raisins, and candied citrus peel, "is a favorite at tea gatherings wherever he is." For a light supper, the couple indulge in a smoked haddock souffle.

Camilla's children still relish their mother's homemade porridge, which she pairs with her own "delicate and mild" honey, according to Parker Bowles. He also revealed that the queen's go-to dish for her family is "roast chicken."

"Afford the best chicken, butter it, add lemon to its cavity, and season it," he said. "She has an Aga stove, ideal for roasting in the U.K. An hour later, it emerges burnished with crispy skin. The meat is juicy. She uses the pan juices as a gravy."

Many individuals believe that British cuisine is unappetizing, but… it's quite straightforward. All you need is a perfectly roasted chicken, asparagus with butter, excellent smoked salmon with brown bread, and sticky toffee pudding. This food is hearty and straightforward.

"Many individuals visit the U.K. and frequent subpar pubs, consume substandard fish and chips that are soggy and unappetizing, and believe that this is representative of British cuisine. However, the key is using the best ingredients, not necessarily the most expensive ones."

Parker Bowles emphasizes the importance of simplicity when it comes to eating like a royal. In his book, he describes the king's pantry as containing "game, beef and lamb," along with seasonal fruits and vegetables such as "peas, strawberries, raspberries and chard."

The king is the most knowledgeable person about food and farming, including British cheeses, rare sheep and cow breeds, and heritage varieties of plum, apple, and pear.

"The king, who has long emphasized the significance of sustainable agriculture, ensures that there is no waste at his table."