Prince Harry certainly has the riches of a royal, but there is one relatable, money-saving habit that he says he's obsessed with: making sure he doesn't have too many lights on at home.

Of course, Prince Harry does it for other reasons than saving money. Harry revealed the quirk is one he learned from his father, Prince Charles, who is well-known for being an advocate for sustainability and environmentalism.

"He's a stickler for turning lights off," Harry says of his father Prince Charles in the new BBC One documentary, "Prince, Son and Heir: Charles at 70," People reports. "And that's now something that I'm obsessed with as well."

"I know, I've got serious OCD on light switches now, which is terrible," adds Prince William.

As a newlywed, Harry acknowledges that even his wife Meghan Markle has commented on the habit.

"My wife certainly 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," Harry says in the documentary.

"And all of a sudden it becomes a habit and those small habit changes he's making, every single person can do," Harry continues. "And I think it's one of the key lessons that he taught us."

Prince Charles and his sons aren't the only energy-savers in the royal family. In the past, it was reported that the Queen had posted warnings signs around the palace that read, "The attention is drawn of all members of staff to the need to switch off unwanted lights. By Order of The Master of The Household." Sometimes, she even reportedly roamed the expansive hall's of the palace, flicking the lights off herself.

Turning off the lights at home is not only good for the environment, it won't hurt your wallet either. The British royal family has been estimated to be worth around $95 billion, but they are still known to pinch pennies when they can, such as buying IKEA, eating leftovers and Prince George wearing his father's hand-me-downs.

Don't miss: Prince Harry reportedly drove this car and now it's for sale on Autotrader for $93,000

Like this story? Subscribe to CNBC Make It on YouTube!