Australian socialite Susan Renouf has been diagnosed with cancer.

The colourful identity, who once dominated fashionable society and has remained a social pages fixture since the 1960s, has been receiving weekly chemotherapy treatment at a private Melbourne hospital, according to News Limited newspapers.

The 70-year-old was diagnosed four weeks ago with the cancer, which is already much progressed, said the report.

A family insider said the news came "as a complete shock".

Lady Renouf, nee Rossiter, is best known for her hats and her husbands - of which there have been three. She married politician Andrew Peacock in 1963, British gambling tycoon Robert Sangster in 1978 and New Zealand financier Frank Renouf in 1985. Frank Renouf died in 1998.