A lawyer for Viktor and Amalija Knavs says the Slovenian couple took the citizenship oath on Thursday in New York City.
The Knavses raised Melania in the rural industrial town of Sevnica while Slovenia was under Communist rule.
They came and went from the ceremony at a Manhattan federal building flanked by Homeland Security police.
Viktor is 74, two years older than President Donald Trump. Amalija is 73.
The first lady, born Melanija, changed her name to Melania Knauss when she started modelling.
Source: news24.com