Hollywood actor Johnny Depp has revealed the "darkest period" of his life was when his daughter Lily-Rose was admitted to hospital with kidney failure.

Speaking to comedian Graham Norton on an episode of The Graham Norton Show, Depp revealed that his sixteen-year-old daughter with ex Vanessa Paradis was admitted to London's Great Ormond Street Hospital (GOSH) for nine days in 2007 for kidney failure caused by E.coli poisoning.

The actor spoke about how he continues to visit hospital dressed up as Captain Jack Sparrow, his famous character from the Pirates of the Caribbean movie franchise, to cheer up patients.

"For me it's a gift. They give me the gift," Depp said, according to reported Daily Mail.

"When my daughter was ill in Great Ormond Street it was the darkest period of my life. I'd always done these visits but after that experience the visits became more and more important."

"The kids are so courageous but to be able to bring a smile or a giggle to the parents means everything in the world to me," the 52-year-old actor added. Depp donated $2 million to the Great Ormond Street Hospital in 2008 after his daughter was successfully treated for the illness.

The actor is in London to promote his new film Black Mass in which he essays the role of crime boss James "Whitey" Bulger.

During the chat he even joked that he had his eyes set on a knighthood after spending a lot of time in the capital.

"I end up here quite a lot. I'm after the 'Sir' thing," the actor said in a report by People Magazine. .

But Depp might have some problems understanding the ceremony if his first meeting with royalty is anything to go by.

"I met Prince Charles. He came to the premiere of Finding Neverland, I shook his hand but I didn't understand a word he said and I don't think he understood a word I said so it wasn't very meaningful necessarily, but he seemed nice!" he said.

The Graham Norton Show will air on November 27 at 10.35 P.M. on BBC One.