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It's a girl for Mark Zuckerberg and his wife Priscilla! On Dec. 1, the couple announced (on Facebook, of course) that they welcomed their first child.

"Priscilla and I are so happy to welcome our daughter Max into this world! For her birth, we wrote a letter to her about the world we hope she grows up in," the Facebook founder captioned a photo of the couple and their newborn. "It's a world where our generation can advance human potential and promote equality -- by curing disease, personalizing learning, harnessing clean energy, connecting people, building strong communities, reducing poverty, providing equal rights and spreading understanding across nations."

He continued, "We are committed to doing our small part to help create this world for all children. We will give 99% of our Facebook shares -- currently about $45 billion -- during our lives to join many others in improving this world for the next generation. Thank you to everyone in this community for all your love and support during the pregnancy. You've given us hope that together we can build this world for Max and all children."

The couple's lengthy letter to Max was equally heartfelt and hopeful.

"Your mother and I don't yet have the words to describe the hope you give us for the future. Your new life is full of promise, and we hope you will be happy and healthy so you can explore it fully. You've already given us a reason to reflect on the world we hope you live in," mommy and daddy wrote. "Like all parents, we want you to grow up in a world better than ours today."

The Zuckerberg's said they have a moral obligation to create a better world for the future.

"We believe all lives have equal value, and that includes the many more people who will live in future generations than live today. Our society has an obligation to invest now to improve the lives of all those coming into this world, not just those already here," the couple wrote. "But right now, we don't always collectively direct our resources at the biggest opportunities and problems your generation will face."

They focus a lot on the hope that Max's generation will find a way to cure disease, advanced human potential and promoting equality.

"If society focuses more of its energy on these great challenges, we will leave your generation a much better world," the letter said.

Mark and Priscilla dated for nine years before getting married in 2012. While announcing in July that they were expecting, Mark openly admitted that Priscilla had several miscarriages while trying to have a child. That makes Max's birth more special for them.

"Max, we love you and feel a great responsibility to leave the world a better place for you and all children. We wish you a life filled with the same love, hope and joy you give us. We can't wait to see what you bring to this world."