Matt Goss says Reggie Kray used to ring him from prison and read poetry down the phone.
The 51-year-old singer has opened up about his unlikely friendship with the notorious London gangster - who was arrested in 1968 along with his twin brother Ronnie and sentenced to life imprisonment the following year - and he even named his French Bulldog after his late pal.
Speaking to comedians Nick Helm and Nathaniel Metcalfe on their FUNBAR Radio 'Fan Club' show, he said: "He was one of my old mates. Reggie used to call me from prison, or as he would say 'calling from Her Majesty's'.
"He used to read poetry and we used to chat. It was an incredible friendship we started to build."
Matt revealed the pair start to get close when Reggie simply called him up and introduced himself over the phone.
He added: "It was a strange one really. I was sitting down at a sushi restaurant and I'll never forget I was like, 'Hello'.
"It was a phone call and he was like, 'Hello Matt'. He was like 'It's Reggie. Reggie Kray'. I'm like, 'Hello, how are you doing Reggie?' It was just one of those moments!"
While Ronnie died from a heart attack in Broadmoar Hospital in 1995, Reggie served his sentence until he was released from prison on compassionate grounds in 2000 - just eight a half weeks before dying of bladder cancer.
Matt said: "He was a very interesting man and full of things that he wanted to do. Remember, he did serve 30 years. He did his time.
"I went to visit him at Her Majesty's and he was just a very, very nice man... He wanted to be a clothing designer.
"He had so many things that he wanted to do. He sent me sketches of the designs he wanted to do."
Meanwhile Matt - who also has a twin brother, Luke - explained that part of the reason he and Reggie connected was their siblings.
He revealed: "He said he understood the dynamic of being a twin, and he understood the dynamic of wanting your own identity.
"When you're a twin you possibly overcompensate for your own identity because people think if you break your wrist your brother's going to break his wrist.
"People think you are literally the same person sometimes, but that's not the case."