Mussolini never officially recognised Elena Curti as his daughter.
Elena Curti, the last 'secret daughter' of Italian Fascist dictator Mussolini, died aged 99 at her home north of Rome on Monday.
Her funeral is due to take place on Tuesday in Acquapendente, near Lake Bolsena, where she lived for the last two decades, according to Italian media.
Born on 19 October 1922, days before swept Mussolini to power after the March on Rome, Curti would have turned 100 later this year, newspaper Corriere della Sera reports.
Never recognised officially by ll Duce as his daughter, Elena was born from an affair between Mussolini and Angela Cucciati, the wife of a jailed Fascist militia squad leader in Milan, Bruno Curti.
Angela, a 21-year-old seamstress, had requested Mussolini to solicit the release of her husband from prison.
Mussolini obliged but not before the pair became lovers and Angela became pregnant. Eight months after her husband was freed from jail, Elena was born "prematurely".
At the time of the affair in 1921 Mussolini was the 38-year-old editor of the newspaper Il Popolo d'Italia, however by Elena's birth he had been appointed prime minister by King Victor Emmanuel III, ushering in Italy's Fascist regime.
Angela - who died in 1978 - did not reveal the truth to her daughter until she was 20 years old, reports Corriere della Sera.
"My mother confessed it to me outright one evening after dinner" - Elena is quoted as saying - "I asked her if Mussolini knew. 'Yes, of course, but he prefers that you don't know for now', she replied. From that day on I spent whole days questioning myself in front of the mirror with photos of Il Duce and my papà."
Elena first saw Mussolini as a child, in 1929, at an inauguration ceremony in Milan, reports news agency Adnkronos.
"Mussolini passed between two sections of a cheering crowd" - she recalled in an interview - "he stopped abruptly, looked at my mother for a moment, then bowed his head towards me, smiled and stroked my hair. I had the feeling of being chosen."
The first official meeting between Mussolini and Elena took place on 13 April 1941 at his offices in Palazzo Venezia. She said he gave her books for her studies, often with banknotes slipped inside.
When Mussolini retreated to Salò at Lake Garda in 1943, Elena followed him and was employed as a secretary in one of the Nazi puppet state’s ministries headed by Fascist minister Alessandro Pavolini.
Elena recounted the story in her memoir Il Chiodo a Tre Punti (The Thee-Pronged Nail), published in 2003, and subtitled Fragments of Memory of Il Duce's Secret Daughter.
Mussolini's last mistress, Clara Petacci, allegedly "threw a jealous fit" over Il Duce's interest in Elena, fearing that she was a rival.
In an interview with The Times in 2003, Elena said that somebody, presumably Il Duce, "revealed to Petacci that I was Mussolini's daughter, to shut her up."
When Mussolini was arrested in Dongo on 27 April 1945, along with Petacci and senior Italian Fascist leaders, Elena was among the entourage fleeing towards the Swiss border.
She was the "blonde girl" found in the armoured vehicle with Il Duce, according to news agency ANSA, with Petacci travelling in another car.
Arrested by the partisans, Elena was transferred to Como and remained in prison for five months, reports Adnkronos, before emigrating to Spain to build a new life.
"When Mussolini was shot and I was imprisoned along with others in his entourage, my mother told the tribunal that I was Il Duce's daughter and so spared me a 20-year sentence for collaboration", Elena told The Times.
After resuming her studies in postwar Rome, Elena married Colonel Enrico Miranda, a pilot decorated by Mussolini for his role in the Battle of Pantelleria.
The couple moved to Barcelona and lived there for more than 40 years.
In a 1992 interview with La Repubblica newspaper Elena said: "I have no proof that I am Benito's daughter, and I don't care to prove it, I only have my mother's word."
She recalled that her mother had asked Il Duce for his help in introducing Elena into the world of cinema, a prospect that did not appeal to Mussolini.
"I like Elena - said Mussolini, who always reserved a special affection for her - she has a square jaw like mine ... but no cinema, she is a flower that should not be spoiled", she told La Repubblica.
In 2000 Elena returned to Italy, settling in the hometown of her husband, who died in 2008, giving numerous interviews recounting her past and the dramatic events of Dongo.
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Mussolini's secret daughter dies in Italy at 99
01021 Acquapendente, VT, Italy