The Prince of Wales carries out hundreds of public outings every year, often with a jam-packed back-to-back itinerary.
And it seems that Prince William, 41, has adopted a habit of his father, King Charles.
An insider tells HELLO! that the heir to the throne does not eat on engagements.
Over the years, we've seen William sampling the odd sweet treat or local delicacy, but it seems he's not one to fill his plate at a buffet.
The reason behind it isn't known, but it seems the Prince is just like his father Charles, who famously does not eat lunch.
The monarch's unusual routine was even acknowledged by Clarence House in a list of 70 facts released for the King's (formerly Prince Charles) 70th birthday in 2018.
Without explanation, number 20 on the list of facts was: "The Prince does not eat lunch."
Charles's former press secretary, Julian Payne, spoke about his boss' eating habits, telling The Mirror: "The King doesn't eat lunch; so, an early lesson I learnt when out on the road with him was to have a big breakfast or bring a few snack bars with you to keep you going.
"The working day is pretty relentless. Beginning with the radio news headlines and a breakfast of seasonal fruit salad and seeds with tea."
Learn more about King Charles's daily diet in the clip below...
So with so much packed into their royal diaries, when does William stop for a meal?
Sharing highlights from their day in the West Midlands city on Instagram Stories, a clip showed William and Kate making their way home as they walked through the rail station to catch their train home.
The Princess carried a large tote bag and inside, there appeared to be two brown paper bags and a bottle of water. The carrier bags looked to be from a deli or a supermarket, so it's likely that the pair ate on the train on the way back to London.
William also shared an insight into his daily diet during a visit to Cornwall last November.
During the trip, the father-of-three was quizzed about his nutrition by nutritionist Monique Hyland.
The royal admitted he had started the day off with a healthy breakfast consisting of two eggs, wholemeal toast with butter, apple juice and a cup of tea with milk and sugar.
Monique told Cornwall Live: "He was okay to start with as he had a healthy breakfast, but then he admitted someone had got him a ‘rubbish sandwich’ for lunch, and he had a chocolate brownie and a glass of red wine."
William also told Monique that he had to have a few cups of tea for the caffeine as "the kids keep me up at night".
LISTEN: When royals are portrayed on the big screen - from TV dramas to Hollywood blockbusters