Prince Harry has inherited more than just a royal title from his dad Prince Charles!

The newlywed revealed that he’s “obsessed” with making sure he doesn’t have too many lights on at home — a “small habit” he inherited from his father, who is a longtime environmentalist.

“He’s a stickler for turning lights off,” Harry says alongside his brother Prince William in the new documentary Prince, Son and Heir: Charles at 70, which aired on BBC One on Thursday. “And that’s now something that I’m obsessed with as well.”

William then chimed in: “I know, I’ve got serious OCD on light switches now, which is terrible.”

Meghan and Harry lead

Harry went on to say that his wife, Meghan Markle, has caught on to his habit at their cottage home in Kensington Palace.

Harry said, laughing: “Which is insane because — I don’t know whether your wife doesn’t — 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.’

“And all of a sudden it becomes a habit and those small habit changes he’s making, every single person can do,” he continued. “And I think it’s one of the key lessons that he taught us.

Charles is also getting his grandchildren, including 5-year-old Prince George, involved in conservation. Speaking from his arboretum at his Scottish home of Birkhall for the documentary, Charles gestures to dozens of trees that were planted when the royal was born five years ago, and says: “This is George’s wood.”

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“As I get older, all I really long for is to plant trees,” Charles continues. “I hope it will be quite amusing for George, as they grow up, and he grows up.”

While in Sydney for his royal tour recently, Harry gave a speech at the Australian Geographic Society Awards and referred to speeches given by his father almost 50 years ago that still ring true.

“My father and others have been speaking about the environment for decades — not basing it on fallacy or new-age hypothesis, but rooted in science and facts, and the sobering awareness of our environmental vulnerability,” Harry said. “And while those speeches would sometimes fall on deaf ears, he and others were unrelenting in their commitment to preserve the most valuable resource we have — our planet.”

This article originally appeared on People. For more stories like this, visit people.com.