Prunella Stack, who has died aged 96, was head of the Women’s League of Health and Beauty in the 1930s, when she was known as Britain’s "Perfect Girl"; she took over the League in 1934, at the age of only 20, after the death of her mother, Mary Bagot Stack, who had founded the organisation four years earlier.

Prunella Stack, an early and enthusiastic promoter of physical fitness for women and hailed as Britain’s “perfect girl,” has died at age 96.

Stack died at her home in London on Thursday, the family said in death notices published on Saturday in The Times and The Daily Telegraph. The cause of death was not announced.

Stack was 20 years old when she took over leadership of the Women’s League of Health and Beauty, now known as the Fitness League, in 1935 following the death of her mother, Mary Bagot Stack, the league’s founder.

Part of a wider European movement that promoted exercise for women and staged massive demonstrations of movement, it grew rapidly under her leadership and expanded into Ireland, Australia, New Zealand, Canada and Hong Kong.

Stack had been a fitness model since the age of 13 and newspapers called the lithe young woman “the perfect girl.”

“Brought up as a health and beauty goddess, I was not used to a lack of homage,” Stack wrote in her 1973 memoir, “Movement is Life.”

Recruiting league members for a public display in London in 1935, Stack declared that she wanted “the youngest, and the oldest, fattest and thinnest, most elementary and most veteran, marching side by side.

“Cut out feelings of shyness of self-consciousness,” she exhorted. “They are selfish, fundamentally, and unnecessary.”

Stack’s fame was demonstrated at her wedding to Lord David Douglas-Hamilton in 1938, when 1,500 guests filled Glasgow Cathedral and thousands more young women thronged outside the church.

Douglas-Hamilton, the youngest son of the Duke of Hamilton, died in 1944 when his plane crashed on returning from a military reconnaissance mission.

Her second husband, Alfred Albers, died in a climbing accident in South Africa in 1951 after just nine months of marriage.

She married Irish lawyer and writer Brian St. Quentin Power in 1964. He died in 2008.

Stack is survived by two son from her first marriage. The family plans a private funeral.