Speaking in a new BBC One documentary Prince, Son and Heir: Charles at 70, the Duke of Sussex says: "He's a stickler for turning the lights off."
"And that’s now something that I’m obsessed with as well.”
Prince William then chimed in: “I know, I’ve got serious OCD on light switches now, which is terrible.”
Harry goes on to admit his wife, Meghan, Duchess of Sussex, has caught on to his habit at their cottage 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.”