Clarke will marry Richard Barnbrook, a councillor in Barking and Dagenham and the party's candidate for mayor of London, whom she met after he came to support her during anti-fascist protests of her performances as Giselle in London this January.
Clarke was exposed by the Guardian as a party member late last year. At the time her membership was revealed, she was in a relationship with fellow English National Ballet principal dancer Yat-Sen Chang, a Chinese-Cuban immigrant with whom she has a five-year-old daughter.
"I first met Simone at the stage door," Barnbrook told More4 News. "I gave her a bunch of flowers on behalf of the party."
"After that we met a couple of times and had a laugh and a drink and a joke. We have so much in common - we are both very interested in the arts."
"She's a beautiful lady," Barnbrook said. "We've been going out for over nine months."
"Seven weeks ago I gave her a diamond ring. I'm traditional like that. In the future we will probably get married and have a family," he said.
Clarke has addressed BNP members at an event, according to the party's leader, Nick Griffin and was recently elected a member of the executive board of Solidarity, which she has described as a "British workers' union".
At the time of the protests, Barnbrook told the Guardian, "I don't normally go to the ballet but I'm going to support Simone Clarke. I'm supporting her freedom of expression."
He cited Clarke's relationship with Chang as proof that she was not racist but said he hoped the couple would not have children.
"I'm not opposed to mixed marriages but their children are washing out the identity of this country's indigenous people," he said.
Barnbrook said today he had no reservations about becoming stepfather to Clarke and Chang's daughter, and that his comments in January had been taken out of context.
"It doesn't bother me at all. I knew about Simone's child before I met her," he said.
"If we do end up getting married, as far as I'm concerned, that child will be my child."
Some people "outside the party with connections to more rightwing parties" might be troubled by it, he said, but he insisted he "couldn't give a damn".
"Whatever the heart does is right, regardless," he said.
Clarke joined the company in 1988, and has been one of its principal dancers since 2004.
In an interview soon after her membership became known, she acknowledged she would "be known as the 'BNP ballerina'. I think that will stick with me for life".
She said she had joined in mid-2005 after Chang told her to stop complaining about what she saw on the television news and do something about it.
Encouraged by him, she went online and found the BNP manifesto, she told the Mail on Sunday.
"I am not too proud to say that a lot of it went over my head but some of the things they mentioned were the things I think about all the time, mainly mass immigration, crime and increased taxes. I paid my £25 there and then," she said.
