Welsh singing legend Dame Shirley Bassey is celebrating her 75th birthday.
Since coming to prominence as a 16-year-old in 1953, she has sold about 135 million records.
But biographer John Williams says that while she still "sounds great", Dame Shirley is "certainly winding down".
"We're never going to see another person like that," he told BBC Radio Wales.
Dame Shirley, who was born to an English mother and Nigerian father, was discovered as a teenager while singing in clubs in her native Cardiff.
It was this background of poverty that helped drive her to success, said Cardiff author Mr Williams.
She is perhaps best-known for performing the theme songs to the James Bond films Goldfinger (1964), Diamonds Are Forever (1971), and Moonraker (1979).
His 2010 biography, Miss Shirley Bassey, outlined her rise to stardom from Tiger Bay, the docks area of the city where she was born.
"Coming from the kind of background that she did - and make no mistake, it was a very, very tough upbringing - it really gave her the impulse to get out," he said.
"She started her career before rock and roll. After her initial hits in the 1950s, what she really wanted was to be a film star.
"But, frankly, that was one thing the colour of her skin was never going to allow her to do."
Dame Shirley had kept her career on track despite a number of personal tragedies, including the suicide of her first husband and the death of daughter Samantha in 1985, Mr Williams said.
'Big gala shows'
He added: "All the other divas looked at Shirley as the model of how to do it, of someone who had kept her career going.
"She does sound great, but she is certainly winding down.
He said she now preferred to perform at "big gala shows" like the Royal Albert Hall tribute concert last year to the late film composer John Barry, than touring to promote her work.
Her life story, from childhood in Cardiff to becoming a star on both sides of the Atlantic, has been turned in to BBC drama.