Mark Zuckerberg and wife Priscilla Chan welcome their second child

Facebook CEO Mark Zuckerberg has revealed that he's welcomed his second daughter.

Mark, 33, and his wife Priscilla Chan announced that they were expecting again back in March and have chosen the unusual baby name August for their second child.

To announce her arrival, the couple posted a photo of their growing family on Facebook along with a letter they'd penned for August, telling her that 'childhood is magical' and reminding her that she only gets to be a child once, 'so don't spend it worrying too much about the future.'

https://www.facebook.com/4/posts/10103996712572761/?pnref=story

The letter opens with the couple exclaiming: 'Welcome to the world!' before warning that although the world can be a serious place, 'that's why it's important to make time to go outside and play.'

August's parents then go on to explain that she will be busy when she's older, advising her to 'take time to smell all the flowers and put all the leaves you want in your bucket now.'

The fill her with all their hopes they have, explaining: 'I hope you read your favourite Dr Seuss books so many times you start inventing your own stories' and 'I hope you run as many laps around our living room and yard as you want'.

With a slightly more tongue-in-cheek line, the couple even refer to their hopes that their latest family addition likes sleep: 'And then I hope you take a lot of naps. I hope you're a great sleeper. And I hope even in your dreams you can feel how much we love you.'

'August, we love you so much and we're so excited to go on this adventure with you.'

Mark and Priscilla's firstborn, Max also received a letter the day she was born in 2015, which about the world they hoped to see her grow up in - a world with better education, fewer diseases, stronger communities, and greater equality.