The former The Vampire Diaries beauty gave birth to the tot 12 days before her 25 September (13) due date.
A statement released to Eonline.com reads: "We are beyond thrilled to announce the arrival of our daughter, Elsie Marigold, on September 13th. A little sister for Ella Betsi. We both feel very grateful and very blessed."
Little Elsie's birth came days after sister Ella turned four on 6 September (13).
The couple wed in 2007.