Microsoft co-founder Bill Gates is reducing his stake in the company to just 1.3 percent, after holding 24 percent of the software maker back in 1996. In a filing to the Securities & Exchange Commission (SEC) on Monday, Gates revealed he’s donating 64 million shares of Microsoft worth a total of $4.6 billion. It’s a huge donation, and Bloomberg reports that it’s the biggest since he gave away $16 billion worth in 1999 and $5.1 billion of shares in 2000.

The SEC filing doesn’t reveal exactly where Bill Gates has donated his Microsoft shares to, but Gates has been on a mission to gift his shares and fund the Bill & Melinda Gates Foundation, a charity set up by him and his wife for their philanthropy. Gates usually donates around 80 million Microsoft shares each year, and this latest gift means he’s left with nearly 103 million shares. The SEC filing also reveals that Melinda Gates holds nearly 425,000 Microsoft shares.

If Gates continues to gift shares like he has in the past, then he could reduce his stake in Microsoft to zero in 2019. Former Microsoft CEO Steve Ballmer is still the largest holder of Microsoft stock, followed by Gates and then current Microsoft CEO Satya Nadella.

While the donation is a large amount in monetary terms, Gates still holds the title of richest person in the world. Bloomberg now values Gates at $86.1 billion, down from his previous $90 billion fortune. Amazon founder Jeff Bezos is edging closer, though. The billionaire briefly surpassed Gates last month to become the world’s richest person, before falling back behind Gates after Amazon’s share price dropped.