A.J. Buckley is a proud dad!

The Justified star and his fiancée Abigail Ochse became first-time parents and welcomed a healthy baby girl on Sunday, Jan. 19.

"Greatest moment in my life happened at 136am this morning when my fiancé gave birth to our little angel Willow Phoenix Buckley #ProudDad," the 35-year-old actor tweeted shortly after the birth.

Weighing in at 7 lbs., 5 oz, "both baby, mother and father are doing well," Buckley's rep confirmed to E! News.

After dating for two years, the former CSI: NY star proposed to the oncology nurse on New Years Eve 2012 in front of friends and family while on vacation in Turtle Bay, Napali.