(NEWSER) – Facebook CEO Mark Zuckerberg returned from paternity leave this week, NBC News reports. As a welcome-back gift, he officially became the world's sixth-richest person on Thursday.

According to Bloomberg, his net worth increased by $6 billion on the stock market Thursday, lifting him past the Koch brothers. The 31-year-old is now worth $47.5 billion. He's currently behind only Bill Gates ($77.9 billion), Amancio Ortega ($70.2 billion), Warren Buffett ($59.1 billion), Jeff Bezos ($51.9 billion), and Carlos Slim ($48.6 billion). But those five have all lost money this year to the tune of a combined $19 billion.

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