The actress and her fiancé Martyn Lenoble are expecting, her rep confirms to PEOPLE exclusively.
Applegate, 38, and Lenoble, 41, dated for two years before becoming engaged on Valentine's Day. No date has been set for the wedding.
The Samantha Who? actress says her fiancé, a Dutch bass player, helped her recover after undergoing a double mastectomy.
"I'm very grateful to Martyn for coming along at a time that he did because he's been my rock through all of this," Applegate told PEOPLE last year. "He gave me something to really want to live for and something to smile about."