In an excerpt from her memoir, due to be published next month, Carol Thatcher charts her mother's decline - and describes the day in 2000 that she first understood her mother was being robbed of her memory.
"I couldn't believe it," Carol said in a selection published by The Mail on Sunday. "She was in her 75th year, but I had always thought of her as ageless, timeless and 100 percent cast-iron damage-proof."
Carol said her mother - who is now 82 - used to have a memory "like a Web site," but that dementia, combined with a series of mini-strokes, had opened "a new and frightening chapter in our lives."
"What was most galling was that there was nothing I could do: this cruel disease takes its own course," she said.
Carol said her mother's memories of the time she spent as Britain's leader from 1979 to 1990 remained among the sharpest. Even as she had struggled to recall an article she had just read, she could still engage in a lively discussion about former Soviet leader Mikhail Gorbachev.
Carol said losing her father, Denis Thatcher, in 2003, was particularly hard on her mother, who kept forgetting he was dead.
"I had to keep telling her the bad news over and over again," she said.
Carol Thatcher says the disease has finally begun to eat away at her mother's memories of her time at top of British politics, too, but that her driver said she still perked up whenever he passed 10 Downing St., the official London residence of Britain's prime minister.
Margaret Thatcher largely withdrew from the public eye in 2002 on her doctors' advice, although she still occasionally releases statements. In March she was briefly hospitalized after feeling faint.
Carol Thatcher's book, "A Swim on Part in the Goldfish Bowl: A Memoir," is due to be published in Britain by Headline on Sept. 4.
By Associated Press Writer Raphael G. Satter