Ms Styles was raised by her grandmother, known as "Kate", and grandfather in Napier. She and her grandmother later moved to her mother's house in Mt Eden after her grandfather died.
Speaking to the Herald, Ms Styles said her grandmother had, over the years, hinted that her father was the famous politician - a favourite of Queen Victoria - but never went into details.
"She shared a lot of memories with me about London, the people she'd met there and about her travels in Europe.
"She didn't go into details about her close family at all. She always said that there were two families, because she was ... placed with a very kind family, which was Irish Catholic - the Donovans - but she herself was of a Jewish background."
Disraeli was involved in politics for about 40 years, during which he was Prime Minister for two terms - first from February 1868 to December that year and then from 1874 to 1880.
He was born to Jewish parents and was a key figure in the creation of what is now the British Conservative Party.
Catherine Donovan was raised in London and was "very much looked after", Ms Styles said.
She stayed in London until her early 20s, when she married and moved to Australia with her new husband.
It is believed she was asked to leave the country as her father's political prominence soared.
After her first marriage failed, she met a New Zealand man and moved across the Ditch in the early 1900s.
It is understood she received a regular allowance from Disraeli, indirectly, right up until his death in 1881.
Ms Styles said she suspected her grandmother was being loyal to her famous father by not revealing the full details of her birth.
"Back then ... if a woman had a child in that society, it was awful."
Ms Styles said her grandmother bore a strong resemblance to her father and the family had long known of their affiliation with the politician.
"This was actually quite a hard book for me to write, because I was divulging secrets about my family."
