Excited to share the news, Rossi, 24, called Sheen her "best friend" and "soulmate."
"Yes! We are engaged! He even was a gentleman and got down on one knee," she told E! News. "I was not expecting it at all. ... The ring is classic and beautiful, but I don't have any photos to share just yet. This is the happiest moment of both our lives. He's my best friend and my soulmate."
This will be the fourth marriage for Sheen, whose first marriage to Donna Peele ended in an annulment. He is also divorced from Denise Richards and Brooke Mueller. The former Two and a Half Men star has five kids from his previous marriages, Cassandra Jade Estevez, Lola Rose, Sam, Max and Bob Sheen.