The Duke of Sussex believes we should replace the phrase “mental health” with “mental fitness” as he made his debut on stage in New York.

Prince Harry, 40, said on Monday mental health was a “very, very important subject” that “affects every one of us” as he joined Tessy Ojo, CEO of The Diana Award, for a panel discussion about the global mental health crisis.

Dressed in a dark blue suit and matching tie, he appeared nervous as he walked onto the stage at the Sheraton Hotel in Manhattan to rapturous applause, clutching some notes.

There was standing room only at the Concordia Annual Summit event and attendees quickly pulled out their phones to record videos of Harry walking on stage.

The Duke watched intently as Dr Tessy delivered her opening remarks, as she revealed the Duke had confided in her before the event that he believed the phrase “mental health” should be replaced with “mental fitness”. 

She said: “The Diana award is a living legacy to Diana, Princess of Wales, and usually when I talk about this, I have to try and tell you what who we are, and maybe tell you who Princess Diana is.

“But today I don’t have to do that, because I’m thrilled to be joined today by her son, Prince Harry, the Duke of Sussex.”

Dr Ojo said she was “very grateful” to have the Duke at the event, describing him as “a passionate advocate for mental health”.

Prince Harry said: “This is a very very important subject that affects every single one of us.”

Both Prince William and Prince Harry have long supported the Diana Award, a charity set up to reflect the late Princess’s belief that young people can change the world and the only one to bear her name.

The Duke and Dr Ojo were joined by two young winners of the Diana Legacy Award, Christina Williams from Jamaica and Chiara Riyanti Hutapea Zhang from Indonesia, for a “call for action”.

The event is the first of several for Prince Harry, who has travelled to New York without his wife, Meghan, for a series of high profile events covering a range of his key interests from conservation to sustainable travel and landmines on the sidelines of the UN General Assembly’s high level week.