Facebook co-founder Eduardo Saverin has renounced his US citizenship, according to an Internal Revenue Service report, days before the company's initial public offering.
The news, first published by Bloomberg on Friday, was based on an IRS notice late in April that named people "who have chosen to expatriate."
Facebook plans to raise as much as $10.6 billion (NZ$13.5 billion) in an IPO that is expected to value the company at as much as $96 billion (NZ$122.6 billion).
The offering could leave Saverin, who once owned 5 per cent of the company, with a hefty capital-gains tax bill.
Saverin has sold enough of his Facebook stake that he does not appear in IPO filing documents that list shareholders who own 5 per cent or more of the company, though his holdings are still believed to be substantial.
A spokesman for Saverin did not reply to several requests for comment on why Saverin had renounced his citizenship.
Saverin now lives in Singapore, an Asian city-state that has no capital-gains tax. There is a minimum 15 per cent rate for long-term capital gains in the United States for people in higher-income brackets.
Saverin, who was born in Brazil, was educated in the United States at Harvard, where he co-founded Facebook with Mark Zuckerberg and others.
The question of American citizenship became a bit of a talking point this week as former Republican Presidential candidate Michele Bachmann revealed she had become a dual US-Swiss citizen, then sought to return her new Swiss passport.
Renouncing citizenship is a complicated and lengthy affair involving a signed oath and an appearance before a US diplomatic official, according to the US State Department's website.
Giving up citizenship is an irrevocable act, according to the State Department.
According to the Internal Revenue Service report, those who gave up citizenship last quarter included Philip Radziwill, nephew of Jackie Onassis, the wife of assassinated former President John F Kennedy.