"We're so incredibly happy and in love. We cannot wait to start our lives together," they said in a joint statement to PEOPLE.
McDermott proposed to the former Beverly Hills 90210 star at a Christmas tree farm on Christmas Eve in Toronto, Canada. Dean's sister put out lights for half a mile leading to a table for two surrounded by decorated Christmas trees. McDermott and Spelling rode up in a horse-drawn carriage, then he presented his fiancée with a diamond and sapphire ring.
"It was so magical. All the stars aligned. I have never been happier in my life," McDermott told PEOPLE.
In September, Spelling announced she was splitting from her husband, actor-writer Charlie Shanian, after a year of marriage. The couple wed on July 3, 2004, in an extravagant wedding hosted by Tori's father, television mogul Aaron Spelling, at his 56,000-sq.-ft. Los Angeles mansion. Shanian, seeking spousal support, officially filed for divorce on Oct. 12.
McDermott filed for divorce on Sept. 9 from his wife of 12 years.
"It just happened," a Spelling friend told PEOPLE about their romance. "No one meant any harm to anyone. You can't help who you fall in love with and who you're right with."