Prince William made a number of royal fans unhappy after misusing the word "serious OCD" in a comment.

In BBC's special documentary "Prince, Son & Heir - Charles at 70," Prince William and Prince Harry shared some juicy details about the Prince of Wales that the public might not have known. In one scene, the Duke Sussex and Duke of Cambridge opened up about Prince Charles' constant efforts to be environmentally friendly.

"He's a stickler for turning lights off," Prince Harry said (as quoted by Cosmopolitan). "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 know I've got serious OCD on light switches now, which is terrible," Prince William added.

Prince William's innocent statement, however, did not sit well with some social media users, who took to Twitter to criticize him. "Yes this is gutting but let’s use it to help us! Prince William has a brilliant following, many of whom don’t touch special media. It’s a great chance for awareness to be built upon. Let’s ask for full exposure to the condition rather than a sorry!" Catherine Benfield wrote on Twitter

"Last night Prince William used the term OCD incorrectly on a tv documentary. Yes, this is gutting, particularly since he’s part of @heads_together but let’s use it as a chance to help us! A great chance for awareness raising," she wrote in another post. "It wasn't meant, Prince William has done brilliant."

"Disappointed to see Prince William describe himself as having 'serious OCD' with light switches when what he means is he was taught to be a "stickler" for turning off lights by his father in order to save energy. That's not OCD & to use the term so offhandedly is not cool," another user wrote.

On the other hand, a number of royal fans still support Prince Wiliam by refusing to berate him. However, they hope that Prince William will be more knowledgeable about the issue.

"Prince William using #OCD in the context he did was far from perfect but I refuse to vilify him for it. We all make mistakes - let’s not mistake a language slip up for ill intent, especially when we know his huge support for @heads_together #bekind #allhumans," Lucy Donoughue wrote.

"Let's hope Prince William takes the opportunity to learn from this mistake and educate both himself and the public on the realities of OCD," Luke Evans added.

"Perfectly put @OCDUK The comment was both hurtful and ironic considering all the good work Prince William has done so far. It really doesn't help when such a debilitating and distressing illness is trivialised. I hope Prince William will realise and find out more about OCD," Rowena Shaw posted.