They were imprisoned in the Tower of London
Not after their 1968 arrest but way back in 1952. The twins were held at the tower for a few days due to failing to report for National Service. They were among the last prisoners ever to be held there.
Lucien Freud owed the Krays money
Freud racked up £500,000 in gambling debts to the Krays. (Lucien: great at painting, ropey with cards.) At one point Freud cancelled an exhibition in case the Krays got wind and demanded their cash.
Reggie Kray was nearly a professional boxer
There was a third Kray brother
Their old brother, Charlie Kray, was also a member of their gang "The Firm." However Charlie was the "quiet Kray" and never received the notoriety of Ronnie and Reggie. In 1997 Charlie was convicted of a £39 million cocaine smuggling plot and, aged 70, jailed for 12 years.
Frank Sinatra hired Kray muscle
In 1985, Frank Sinatra was said to have hired 18 bodyguards from Krayleigh Enterprises, which was the Kray twin's protection company.