Alastair Stewart has revealed he is living with dementia and has suffered a series of minor strokes, discovered after he felt "discombobulated".
The broadcaster, 71, retired this year after nearly five decades on air.
Stewart, who previously worked for ITV News and Channel 4, told GB News his health was behind the decision to leave his full-time role with the channel.
He hosted his final episode of Alastair Stewart And Friends, a discussion programme on GB News, in March.
He explained to former colleague Camilla Tominey he had been diagnosed with early onset vascular dementia.
"The headline story, and it is relatively dramatic, I suppose, is that about six, nine months ago, I began to feel one of my favourite words: a bit discombobulated," he said.
"I wasn't becoming forgetful but things like doing up your shoelaces properly - that's how I wear these lovely moccasins now - making sure your tie was straight, remembering that the call time for your programme is four o'clock and not five o'clock, not turning up early or late, and stuff like that."
Stewart said that, after explaining his concerns to his GP, a scan revealed he had experienced a series of "minor strokes that are called infarct strokes" - though he said he had "no idea" they were happening.
A former presenter of the year, he hosted a range of news and current affairs programmes for more than 35 years. He was awarded an OBE in 2006.
He left his role as a lead presenter at ITV News in 2020 due to what producer ITN said were "errors of judgement" .
Stewart, from Hampshire, joined ITN as industrial correspondent in 1980, before becoming a foreign correspondent and going on to anchor news programmes for ITV and Channel 4.
According to the NHS, vascular dementia is caused by reduced blood flow to the brain, and is estimated to affect around 180,000 people in the UK.
Urging people with similar symptoms to see their doctors, Stewart added that the issue he has found most difficult is the impact on his wife Sally, with whom he has four children.
"We've been married for nearly half a century, and, you know, your life partner, your lover, all of those descriptions that are personal and intimate, that person is reduced - I choose my words very carefully - almost to a carer," he said.
What is vascular dementia and what are the symptoms?
Vascular dementia is a common type of dementia caused by reduced blood flow to the brain.
Slowness of thought
Difficulty with planning and understanding
Problems with concentration
Changes to your mood, personality or behaviour
Feeling disoriented and confused
Difficulty walking and keeping balance
Symptoms of Alzheimer's disease, such as problems with memory and language (many people with vascular dementia also have Alzheimer's disease)
These problems can make daily activities increasingly difficult and someone with the condition may eventually be unable to look after themselves.
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