"We couldn't be more thrilled to be starting a family together," Stone told People.
"We are over the moon."
Stone -- who appears regularly on The Biggest Loser, served as a judge on NBC's America's Next Great Restaurant earlier this year, and also competed on The Celebrity Apprentice's third season last year -- and the 34-year-old actress began dating in 2009.
In February, Stone had stated he was thrilled how his relationship had been progressing, considering the pair's hectic schedules.
"It has been awesome. She is a real sweetheart and I am lucky to have found her," Stone told the Herald Sun at the time.
"She is a busy girl with work, too. She has been juggling a million things as have I."