Maksim Chmerkovskiy and Karina Smirnoff
Roger Karnbad/Celebrity Photo
02/10/2009 at 05:00 PM EST
Maksim Chmerkovskiy may be known as the "bad boy of the ballroom" on ABC's hit Dancing with the Stars,
but when it came time to pop the question
to girlfriend – and fellow DWTS
pro – Karina Smirnoff, his trademark swagger dissolved.
"Planning the proposal was the most nerve-wracking thing of my life," the dancer, 29, tells PEOPLE in its new issue. "When it came down to it, I thought, 'It's not a given that she'll say yes.' All of a sudden it's like, 'I have nothing to say! Why did I even do this?' "
Adds Smirnoff, 31: "I thought it was so cute because you never see Maks [nervous] like this."
Although they only started dating in late September, the Ukrainian-bred couple – who will square off against each other in the new season
debuting March 9 – actually have a long history: They first met as teenagers on the pro dancing circuit.
"You know how boys tend to develop slower than girls?" asks Chmerkovskiy. "A lot slower!" says Smirnoff. Back then, she adds, "I never looked at him seriously."
Now the couple, who plan to wed in late 2009, are looking ahead to starting a family. "Our kids would be rock stars," says Chmerkovskiy, playful swagger back in place. "They're going to be like royalty."
For more on this story, pick up the new issue of PEOPLE, on newsstands FridayRELATED ARTICLE:
Maks had 'difficulty forming sentences' says Karina of his proposal