Prince Harry has revealed the household "obsession" he now lives by after it was drummed into him and Prince William by his environmentalist father King Charles.
The duke admitted that at first his strange habit was something that baffled his wife Meghan Markle who was left confused by his behaviour, the Mirror reports.
He has since explained his reasoning behind his eco-friendly manner in the 2018 documentary 'Prince, Son and Heir: Charles at 70'. The father-of-two shared that he has an obsession with turning off all the lights in rooms when they are not in use and only using limited lighting when it's dark — a trait shared by his older brother William.
"He's a stickler for turning lights off," shared Harry about his dad in the documentary.
"And that's now something that I'm obsessed with as well, which is insane because actually, my wife goes 'Well, why turn the lights off? You know it's dark'.
"I go 'we only need one light, we don't need like six', and all of a sudden, it becomes a habit and those small habit changes he's making, every single person can do. And I think that's one of the key lessons certainly that I felt that he taught us."
It's widely known that the King is an advocate for environmental and green issues and is also said to be keen not to waste money in the monarchy.
It was recently reported that he left palace staff shivering after he turned down the thermostat in Buckingham Palace in a bid to save more energy.
The King has also dropped the temperature of the Palace swimming pool with staff who have permission to use the pool noting it is definitely a lot colder, a source has claimed.
They told The Sunday Times : "A few people using the pool have noticed that the temperature of the water has dropped, and it is quite a bit cooler than it used to be. They have been told the King has had the heating turned down."
The pool was commissioned by King George VI in 1938 to ensure privacy for his daughters Princess Elizabeth and Margaret who had been learning how to swim at a nearby Bath Club.
Now the new monarch is apparently eager to reduce the royal household's staggering energy use which has been a priority of his in recent years.
His Majesty has also recently installed solar panels at his London residence, Clarence House and at his country home Highgrove in Gloucestershire where wastewater is used in the gardens for the plants and flowers.
Don't miss the latest news from around Scotland and beyond - Sign up to our daily newsletter here.