Mark Zuckerberg and wife Priscilla Chan will be adding another girl to the family. Zuck announced the pregnancy Thursday on Facebook, writing that after their "difficult experience" having Max, their first daughter, they didn't know what to expect with regard to future children. "When Priscilla and I first found out she was pregnant again, our first hope was that the child would be healthy. My next hope was that it would be a girl. I cannot think of a greater gift than having a sister," he writes, noting that both he and Priscilla grew up with sisters. "We can't wait to welcome our new little one and do our best to raise another strong woman." Max is 15 months old, People reports. (More Mark Zuckerberg stories.)