It’s no secret that Princess Diana and King Charles III (then-Prince Charles) had a tense marriage—it did end in an affair and divorce after all. There were certain things that the former royal couple just couldn’t see eye to eye on. According to former palace chef Mervyn Wycherley, one point of contention was their sons Prince William and Prince Harry’s diets.

Growing up in Kensington Palace meant the two brothers had all of their meals cooked for them by chefs including Wycherley, who served in this role for 33 years. Wycherley recently joined royal protection officer Ken Wharfe for an appearance on the Sun’s “Royal Exclusive” show, during which he opened up about the family’s eating habits.

“Diana really wanted to experiment away from Mervyn’s food at the palace at that time,” Wharfe said.

Diana gave them this taste of normal life via trips to theme parks and even stops at McDonald’s. However, according to Wharfe, Charles was “very peculiar about the food that he wanted his family and the staff to eat.” He added that the monarch believed “the army marched on its stomach.”

Former BBC reporter Jennie Bond elaborated on this in a column for i Paper: “I remember William’s mother, Diana, telling me that she wanted her two boys to be brought up in a way no other royal princes had been,” she wrote. “She did her best to give them an idea of what life beyond the palace walls is like.”

Wharfe recalls Charles appearing especially bothered by William’s food choices as he aged.

“As William got older, of course, he was very keen to go to burger bars and pizza places, but that didn’t really sit that comfortably with his father,” the protection officer said. Wharfe and William once returned from a pizza and burger establishment on Kensington High Street and were met with disapproval from Charles.

“‘Oh papa we just had these amazing burgers,'” the security guard recalled William saying. “There was this sort of look of disdain with him across the prince’s face,” he continued, adding that Charles said, “‘I don’t know why you eat that food when I have this marvelous army of chefs at Kensington Palace.”

Wycherley explained that Harry and William “really didn’t often [eat out at restaurants], because all of their friends used to do it.” Instead, they “stuck at home and had real nursery food. It was the old treacle tarts and things like that.”

While Diana enjoyed dining out, both Wharfe and Wycherley said she often hung out and ate in the kitchen.

“It was part of Diana’s character, because she had this sort of very friendly approach to all members of the staff actually, and the kitchen—like in everyone’s house really—is a focal meeting point for life,” Wharfe shared.