"They were engaged over the holidays and are very happy," her rep told People.
The news comes just hours after the announcement that Natalie Portman is not only engaged, but also pregnant.
People said Rimes was spotted Monday on Malibu beach, wearing an engagement ring it described as a "platinum sparkler features a 5-carat oval diamond set in rose gold fleur-de-lis connected to the band."
According to the mag: "'The couple wanted an antique feel, but a new ring,' says [a] source, who adds that Rimes and Cibrian designed the ring together with the actor's childhood friend Brent Polacheck at Polacheck Jewelers."
Rimes, 28, and Cibrian, 37, created a tabloid sensation when each left their previous spouse to be with each other after they met filming the Lifetime television movie, "Northern Lights."