Mark Zuckerberg celebrates National Sibling Day with throwback photo of himself with his three sisters

Yesterday was National Sibling Day in America and celebrities took to social media to post old and new photos of themselves and their brothers and sisters. Facebook CEO Mark Zuckerberg shared a photo of himself and his siblings as kids from the 1980s. "Happy Sibling Day to my three wonderful sisters. Here we are having a great time and rocking our awesome 1980s ski jackets." he captioned the photo