CSI: NY actor A.J. Buckley is expecting a baby girl with his pregnant fiancee, Abigail Ochse Credit: John Parra/Getty Images

A.J. Buckley is getting ready to tackle a new role: father! The CSI: NY actor's fiancee, oncology nurse Abigail Ochse, is five months pregnant with the couple's first child, a rep tells Us Weekly.

The engaged pair "are expecting a little baby girl," the rep says. They "look forward to welcoming their new addition in early 2014."

Buckley himself tweeted about the news on Tuesday, Sept. 3. "I'm having a baby girl!!! Happiest day of my life," he wrote, alongside a sonogram of his daughter-to-be. Later, he added: "Thank you for all the kind wishes! So excited to be a dad."

The 35-year-old actor proposed to Ochse on Dec. 31, 2012, while on vacation with friends and family in Hawaii. As previously reported, he popped the question under a tree in Turtle Bay at Napili Beach, where the couple had left some of his late father's ashes the year before. (Joe Buckley died of pancreatic cancer in 2011.)

The CSI: NY actor will next be seen in the movie North of Hell. Katherine Heigl and Patrick Wilson also star.