Boris Johnson has turned in his U.S. passport.
Britain's colorful foreign secretary is on a new U.S. Treasury list of Americans who have renounced their citizenship.
Johnson, who previously served as the mayor of London, was born in New York to British parents. Johnson left the U.S. when he was five years old, but the former journalist remained a dual citizen.
It's not clear exactly when Johnson renounced his allegiance to the U.S.: The Treasury list is published quarterly, but it can take months for names to appear on the document.
Johnson wasn't always happy being American. In 2015, he settled a U.S. tax bill that he had described as "absolutely outrageous."
Unlike most countries, the U.S. taxes its citizens on all income, no matter where it's earned or where they live. The rules can sometimes result in surprise tax bills for Americans who live abroad.
Johnson had initially refused to pay the bill, saying the IRS was "coming after him" for capital gains tax on the sale of his first London home.
Johnson, a Conservative, was appointed foreign secretary after Britain voted to leave the European Union -- a result he campaigned for after wrestling with his fears that it could cause an economic shock and break up the U.K.
Related: Boris Johnson's best put-downs
Often disheveled but always outspoken, the Briton makes for an unlikely chief diplomat: He once described Barack Obama as a "part-Kenyan President" with an "ancestral dislike of the British Empire."
More recently, he suggested he would avoid visiting New York because of "the real risk of meeting Donald Trump." He has also likened Hillary Clinton's appearance to that of "a sadistic nurse in a mental hospital."
Prime Minister Theresa May slapped him down for accusing ally Saudi Arabia of "puppeteering and playing proxy wars" in the Middle East.
Related: Record number of Americans dump U.S. passports
Johnson is one of an increasing number of Americans who are cutting their ties to Uncle Sam.
Many of those severing links are expatriates who are tired of dealing with complicated tax paperwork, a headache that has worsened since new regulations came into effect.
Johnson is listed in the Treasury document as Boris Alexander Johnson. His full given name is Alexander Boris de Pfeffel Johnson.
