The filing did not name the recipient. But in most circumstances, if the gift were made to a relative or a family trust, that fact would be disclosed.
So we're thinking Sandberg, who has championed nonprofits seeking to improve the position of women in society, may have made a charitable donation.
She's on the board of Women for Women International and V-Day, and serves on the advisory board of the Somaly Mam Foundation.
The gift is a substantial portion of her total holdings, which were worth $720 million at last count.
We asked Facebook who the recipient is.
"I'm sorry, we aren't disclosing that," a representative told us.
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