Facebook founder Mark Zuckerberg and his wife Dr. Priscilla Chan has one very important reason to celebrate. The couple have welcomed their first child together, a daughter named Max.

Zuckerberg announced the news himself on Facebook, in a letter to his daughter that celebrated Giving Tuesday. “Your mother and I don’t yet have the words to describe the hope you give us for the future,” he writes. “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.”

As part of the letter, Zuckerberg announces the launch of the Chan Zuckerberg Initiative, which will seek to cure diseases and connect people around the world, among other things. With that, Zuckerberg also reveals he and Chan will be giving 99% of their shares in Facebook — currently valued at $45 billion — to the initiative.

“We know this is a small contribution compared to all the resources and talents of those already working on these issues,” Zuckerberg says. “But we want to do what we can, working alongside many others.”

Ending his letter with hope for the future, the Facebook head writes, “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.”