Former England footballer Gordon Banks and Sir Michael Parkinson have relived their heartbreaking personal experiences with dementia to inspire the nation to reduce the stigma about the condition.
The pair, alongside broadcaster Fiona Phillips, are also encouraging people who think they have any symptoms of the condition to seek medical advice.
New research from Alzheimer's Disease International (ADI) found that a quarter of people hide their diagnosis because of negative connotations surrounding dementia.
Phillips, whose parents both had dementia, said if her mother had been diagnosed earlier then she could have handled the situation better.
"I would have been able to plan more for mum instead of doing everything in a big rush," she said.
"Our house always smelt of baking when we were little and I used to love helping mum make cakes and there were always cakes in the tin.
"She rung me up at 3am one morning crying her eyes out and she said: 'I've forgotten how to make cakes'. And my childhood went then."
Sir Michael said: "The ultimate problem you have to face with anyone who has any form of dementia is that you lose them before they die.
"I lost my mother 18 months to a year before she died and that is the ultimate desperate tragedy."
Banks, whose brother David suffered from the condition, recalled: "We sat in the lounge talking to him and we would ask him a question and he would just go blank - he wouldn't answer it - he couldn't remember what we were discussing."
The trio have joined a government campaign to increase early diagnosis rates for dementia.
The new campaign, which is part of Prime Minister David Cameron's pledge to help change people's understanding of dementia, has been launched today on World Alzheimer's Day.
Ministers hope it will raise awareness of the condition, what initial signs and symptoms look like and how to seek help.
Mr Cameron said: "Dementia is a devastating disease that puts enormous strain on people and their families.
"Shockingly, nearly 400,000 people are unaware that they have the condition and so we want to make sure more people know what dementia is and how to spot those tell-tale signs.
"With the number of sufferers set to rise in the years ahead, I am determined that we go much further and faster on dementia.
"That's why I launched a Challenge on Dementia in March, doubling the research budget and working across society to improve health and care, and supporting people to live well with the condition."
Health Secretary Jeremy Hunt added: "Our goal is to make this country a world leader in tackling the challenge of dementia.
"That requires us all to play our part, including being brave enough to start conversations about dementia to get our loved ones the early help we know makes a difference.
"Awareness is just the first step towards tackling the stigma around this condition and we need to work together if we're going to help those living with dementia have a better quality of life."
Jeremy Hughes, chief executive at the Alzheimer's Society, said: "Talking to a loved one about dementia will probably be one of the most difficult conversations you ever have, but it will be worth it.
"Early diagnosis is crucial in helping people with dementia to access the support and help they need to live well with the condition."
Research, released today by the ADI, also found that three quarters of people and 64% of carers believe that there are negative associations for those diagnosed with dementia.
The report, based on a survey of 2,500 sufferers and carers from 50 countries, also found that two-fifths of people say they have been avoided or treated differently because they have dementia.
Marc Wortmann, executive director at ADI, added: "Dementia and Alzheimer's disease continue to grow at a rapid rate due to global ageing.
"The disease has a huge impact on the families that are hit, but also affects health and social systems because of the economic cost.
"Countries are not prepared and will continue not to be prepared unless we overcome the stigma and enhance efforts to provide better care for those who have dementia and find a cure for the future."
Initial signs of dementia, which is caused by diseases of the brain, may include short term memory loss that affects every day life, problems with thinking or reasoning or unexplained anxiety or depression.
The UK's dementia research charity has also pledged to give £5.5 million to fund scientists researching the condition.
Alzheimer's Research UK said the money will go towards 52 new grants aimed at understanding the causes of dementia, improving diagnosis and finding new treatments and preventions.