ITV's new three-part documentary series, Secrets of the Krays, makes its debut on Tuesday night and takes an in-depth look at the most famous gangsters in British history.
MORE: Grantchester star Robson Green gives major update on season seven
Once rulers of the criminal underworld, the Kray twins lived a fascinating life filled with corruption and violence. Want to know more? Read up on some interesting facts about the brothers, as well as answers to frequently asked questions…
WATCH: Will you be watching the new documentary series?
1. They were among the last prisoners of the Tower of London
The twins were among the last prisoners to be held at the Tower of London in 1952 after they failed to report for national service. The pair were held there for a few days, joining a long list of notable criminals to be kept there, including Guy Fawkes and Rudolf Hess.
2. They were fans of poetry
It may come as a surprise to learn that two of the UK's most notorious gangsters were fans of poetry. According to childhood friend Laurie O'Leary, the twins enjoyed writing their own poems. Their cousin, Kim Peat, also revealed that Reggie used to send her poems that he had written from prison.
MORE: Breaking Dad: viewers stunned by 'insane' stunt in episode two
MORE: Charlotte Church opens up about stepfather's devastating rare illness
3. The brothers were rumoured to be bisexual
Ronnie discussed his homosexuality with very few people, according to Laurie O'Leary. However, in his 1993 book My Story he stated: "I'm bisexual, not homosexual. Bisexual."
The Krays were two of the most notorious gangsters in British history
Ronnie was also rumoured to have a sexual relationship with Conservative politician Lord Boothby.
While Reggie was believed to be bisexual, he habitually denied it.
4. Frank Sinatra hired bodyguards from the Krays
In 1985, Frank Sinatra is said to have hired 18 bodyguards from the Krays' lucrative bodyguard and 'protection' business, Krayleigh Enterprises.
5. Reggie could break a jaw with one punch
Reggie had a deadly signature punch and is said to have broken the jaws of his victims with just one hit.
MORE: Nightmare Alley: viewers saying the same thing about Bradley Cooper's new film
He would offer a cigarette to his victim and as they put it in their mouth, he would strike their jaw.
6. Ronnie suffered from schizophrenia
By the time of his murder trial at the Old Bailey in 1969, Ronnie had battled with schizophrenia for 16 years. A doctor notes that "if he does not have his tablets he becomes very depressed and suspicious and thinks that people are trying to injure him," according to The Guardian.
Reggie married Frances Shea in 1965
7. Reggie kept a scrapbook of all the times they appeared in the press
Over a period of 15 years, Reggie would keep newspaper clippings in a scrapbook every time the brothers appeared in the press. Reggie kept articles that detailed his and his brother's early crimes in the 1950s.
When did the Kray twins die?
Ronnie remained in prison until his death on March 17 1995, while Reggie died on 1 October 2000 of cancer, eight and a half weeks after being released from prison on compassionate grounds.
MORE: The Responder: viewers spot plot hole in episode one
Are there any Krays still alive?
Cousin of the Kray twins, Kim Peat, spoke to The Mirror in May last year about the gangsters.
Kim Peat sent letters to her cousin Reggie while he was in jail
Kim's grandmother, May, was the sister of Ronnie and Reggie’s mum, Violet, and she grew up next door to the family. She even visited the pair while they were in jail and sent letters and poems to Reggie every other day.
While she wasn't proud of her cousin's criminal activities, she was devastated when Reggie died of cancer.
Did the Kray twins have children?
Neither of the brothers had children. Charlie Kray, their older brother, was the only one to have a child, a son named Gary.
MORE: Outlander drops major plot hint for season six - but fans are divided
What did the Kray twins own?
The Kray twins owned a nightclub in Wilton Place, Knightsbridge called Esmeralda's Barn from 1960 until its closure in 1963.
The Kray twins enjoyed writing poetry
They also bought a pub in Bethnal Green called The Carpenters' Arms as a gift for their mother, Violet, in 1967.
Secrets of the Krays begins on Tuesday 25 January on ITV at 9pm.
Like this story? Sign up to our newsletter to get other stories like this delivered straight to your inbox.