Lady Thatcher has had a series of strokes
The daughter of former UK prime minister Margaret Thatcher has spoken for the first time about her mother's struggle with dementia.
In her new book, serialised in the Mail on Sunday, Carol Thatcher says she first noticed her mother's memory was failing over lunch in 2000.
She says she "almost fell off her chair" seeing her mother, 82, struggle.
Ms Thatcher also says Baroness Thatcher had to be reminded several times her husband, Sir Denis, had died.
In her book, A Swim-On Part in the Goldfish Bowl: A Memoir, she tells of how her mother's "blotting-paper brain", which had always absorbed information, began to fail eight years ago - a decade after leaving power.
The former Conservative prime minister got confused between Bosnia and the Falklands during a conversation about the war in the former Yugoslavia, Ms Thatcher writes.
"I almost fell off my chair. Watching her struggle with her words and her memory, I couldn't believe it," she says.
"She was in her 75th year but I had always thought of her as ageless, timeless and 100% cast-iron damage-proof."
The contrast was all the more striking because she had always had a memory "like a website", she writes.
Ms Thatcher goes on to describe how telltale signs of dementia then began to emerge.
"Whereas previously you would never have had to say anything to her twice, because she'd already filed it away in her formidable memory bank, Mum started asking the same questions over and over again, unaware she was doing so.
"It might be something innocuous - such as 'What time is my car coming?' or 'When am I going to the hairdresser?' - but the fact she needed to repeat them opened a new and frightening chapter in our lives."
Ms Thatcher says her mother retains good long-term memory
Ms Thatcher describes how she had to learn to be patient and that her mother "had an illness and that it wasn't personal".
"That's the worst thing about dementia: it gets you every time," she says.
"Sufferers look and act the same but beneath the familiar exterior something quite different is going on.
"They're in another world and you cannot enter."
Losing Sir Denis to pancreatic cancer in 2003 "was truly awful" for her mother, she says, "not least because her dementia meant she kept forgetting he was dead".
"I had to keep giving her the bad news over and over again.
"Every time it finally sank in that she had lost her husband of more than 50 years, she'd look at me sadly and say 'Oh', as I struggled to compose myself.
"'Were we all there?' she'd ask softly."
Series of strokes
On bad days her mother can "hardly remember the beginning of a sentence by the time she got to the end", she says.
But on good days there are flashes of her old self, and she retains a good memory of her time in office "as if her dementia had sharpened her powers of long-term recall", she adds.
Lady Thatcher, who was prime minister from 1979 to 1990, had a series of minor strokes in 2002 and was advised by doctors to stop making public speeches.
Friends of the Tory peer, who lives in central London, said earlier this year the strokes had affected her short-term memory.
But Ms Thatcher's book is believed to be the first time a family member has spoken publicly of her condition.
Lady Thatcher briefly returned to the limelight in September last year when she visited Downing Street as a guest of Gordon Brown.
She had won praise from the prime minister who described her as a "conviction politician".