The professional dancer, who partnered Gavin Henson in the most recent series of the BBC1 hit show, is to take the plunge with Danish dancer and coach Klaus Kongsdal.
Virshilas has told Hello! magazine that he surprised her with a romantic proposal after she rehearsed for the final last month.
"I opened the door and there were hundreds of rose petals and candles," she said.
"My first thought was 'oh my God, I forgot our anniversary or something' because for the past three months I had been so absorbed with Strictly."
Virshilas, who partnered Phil Tufnell in 2009, said working on Strictly absorbed her life completely.
It was Henson – rather than Kongsdal – who captured her first waking thought each day.
"Every single morning when I was waking up, I was thinking about Gavin, even if it was only how to make his falls softer, and his highs higher."
However, her real-life partner said he was not at all jealous of the time she spent with the rugby star. "It was funny, because in the first few weeks I said to Gavin: 'You've got to grab her, come on, you've got to look like you're going to kiss her'.
"Gavin was looking at me as if to say, 'are you nuts?'. But I have to say that Gavin is such a great guy that I never had any reason to be worried," added Kongsdal, a former European champion and one of the main coaches for the Danish ballroom team.
Lithuanian-born Virshilas, who was raised in Israel and Canada, has been dating her fiance for 14 months. They met in the BBC bar after recording a show in 2009.
Kongsdal told Hello! he had planned to propose for months, although he was determined to wait until her commitments to the show had wound down.
"The biggest deal for me was that she had to be finished with Strictly first, because it takes over so much of your life," he said.
The pair have also tried to get Henson back in the dating game after he split from Charlotte Church, with whom he has two children.
Virshilas said she had set him up with a friend of hers, but added: "I tried once and he said 'don't try again'."