Bruce Willis has lost his "joie de vivre" amid his ongoing health battle.

The 'Die Hard' actor has Frontotemporal dementia (FTR) - an uncommon form of the disease which causes a deterioration in personality, behaviour and language - and his friend Glenn Gordon Caron admitted the star's joy for life "is gone" as he appears to be "seeing life through a screen door".

He told the New York Post: “My sense is the first one to three minutes he knows who I am. He’s not totally verbal.

“He used to be a voracious reader — he didn’t want anyone to know that — and he’s not reading now.

"All those language skills are no longer available to him, and yet he’s still Bruce.

"When you’re with him you know that he’s Bruce and you’re grateful that he’s there, but the joie de vivre is gone.”

The 69-year-old director - who created 1980s comedy drama 'Moonlighting', which starred Bruce alongside Cybill Shepherd as private detectives - explained how the 68-year-old star really "loved life" and tried to live it "to its fullest" before his diagnosis.

He added: “The thing that makes [his disease] so mind-blowing is [that] if you’ve ever spent time with Bruce Willis, there is no one who had any more joie de vivre than he.

"He loved life and … just adored waking up every morning and trying to live life to its fullest.”

Glenn revealed he has tried to visit his friend almost every month since his aphasia diagnosis.

He said: “I’m not always quite that good but I try and I do talk to him and his wife [Emma Heming Willis] and I have a casual relationship with his three older children.

“I have tried very hard to stay in his life.”