Lady Sonia McMahon, the glamorous widow of former prime minister Sir William McMahon and mother of Hollywood-based actor Julian, has died in Sydney, a hospital spokesman said on Saturday.
McMahon, who created headlines in 1971 when she wore a daring white dress with splits up both sides to a White House dinner with Richard Nixon, had been suffering from cancer.
"Lady Sonia McMahon passed away late last night," a spokesman for St Vincent's Private Hospital said.
"She died peacefully with her family by her side."
McMahon worked as an occupational therapist before she married her husband -- who was 24 years her senior -- in 1965.
During her husband's term as prime minister she attended a White House dinner held in his honour wearing a floor length gown slit to the thigh and held together from there to under the arm by thin rhinestone-studded straps.
Asked about the incident later, she said: "Well, there are worse things I could be remembered for, I guess."
"We used to go to continuous dinners and have to wear long dresses and I got so sick of all those ordinary sort of dresses that I thought, 'Oh, I can't stand it any more', and so this was a light relief." Prime Minister Kevin Rudd paid tribute to McMahon, describing her as a "distinguished representative of Australia".
The 77-year-old had been a fixture on Sydney's social circuit until hit by skin cancer and other ailments over the past 18 months.
She is survived by her three children -- daughters Melinda and Deborah and actor son Julian, who played one of the lead roles on US television show "Nip/Tuck".
William McMahon was prime minister from 1971 to 1972 and although he retained his seat in parliament until his retirement in 1982 he is remembered as one of the country's least popular leaders. He died in 1988 aged 80.