Former TV newsreader John Suchet revealed the torment caused by his wife's dementia today, saying: "It's as if she has died."
The broadcaster said the disease had "taken" Bonnie, his wife of 24 years, since she was diagnosed with Alzheimer's disease three years ago.
"The past we shared is a closed book to her," he said in an interview with the Daily Telegraph. "The Bonnie I loved has actually gone. It's as if she has died. Dementia has taken her."
Suchet, 64, said his wife now needed to be dressed and no longer knew which families their five grandchildren belonged to. It has also been many months since she had gone out or even cooked.
These had prompted suicidal thoughts, he said, adding that until now he had kept her condition a secret from all but family and close friends.
The former ITN stalwart, who currently presents quiz show Going For Gold on Five, said: "There are times I want to bury my head in my hands. When I persuade myself she would be better off without me because I'm crap at handling this. You have suicidal moments."
Suchet said the first sign his wife, 67, was suffering from a serious illness came four or five years ago while they were waiting for a flight to France. She went off to the nearby ladies toilet, but was unable to find her way back to her husband.
On a later trip to the United States, she passed out in a restaurant.
Then three years ago she was referred to a neurologist in London, who diagnosed Alzheimer's disease.
"It was a relief because I knew by then that it was something serious," he said.
"I said: 'Don't worry. Everything's fine.' And she believed me. Still does.
"The only good thing about this...disease is that it protects the person from what is going on."
He contrasted Alzheimer's with cancer, saying if she was suffering from the latter they could still be intimate and would be "figuring how to fight the bloody thing".
Suchet added he now had some in-house assistance to help look after his wife at their London home.
Suchet said the Admiral Nurse who helped to care for his wife had "probably, quite literally, saved my life".
He told BBC Breakfast that everyone who cares for someone with dementia should have access to one of the nurses, but added that there were only 60 across the country.
Referring to the disease, he said: "In only a few years' time it's going to be what cancer was a generation ago. Now, if you're diagnosed with cancer, you can talk about it and say 'We're going to beat it.'
"We're not there with dementia yet. I don't know when we will be, it's going to be a very long time."
He added: "It's devastating. The most difficult thing for me is that Bonnie doesn't know she's got it and that's the unique quality of this awful, awful disease.
"Uniquely for this disease, the full weight falls on the shoulders of the carer and they need help."
Neil Hunt, chief executive of the Alzheimer's Society, said: "It is deeply distressing that John Suchet has been pushed to the brink in his efforts to deliver the best care for his wife.
"Like John, many carers need more support. Dementia is not just a natural part of ageing; it is a physical condition of the brain that robs people of their lives.
"Sadly, John and Bonnie are not alone. As the population ages over a million of us will be diagnosed with dementia in the next 10 years.
"We urgently need to invest more to care for people today and find a cure tomorrow."
Harriet Millward, deputy chief executive of the Alzheimer's Research Trust, said: "By speaking so frankly about his wife's experience, John Suchet has highlighted the toll dementia takes on the 700,000 people in the UK, and their families, who live with it.
"Dementia costs our economy £17 billion a year - £6 billion of which is absorbed by carers - and radical reform is urgently required.
"The long-term solution to our dementia crisis is to invest in research.
"Dementia research is severely under-funded in the UK, receiving eight times less government support than cancer."