Michael Wildes, the couple's immigration lawyer, confirmed they took the oath of citizenship on Thursday.
"It went well and they are very grateful and appreciative of this wonderful day for their family", the couple's immigration attorney, Michael Wildes, said.
Advocates for restricting legal immigration have pointed to the imbalance in favour of family connections as evidence of the need for reform, calling for a "merit-based" system that would choose immigrants based on need in the US. Her husband, Donald Trump, has proposed ending most family-based immigration, which he refers to as "chain migration". I've had the privilege of coming to this building for more than 30 years working with some of the finest families and individuals [.] This golden experiment, these doors that are in America, remain hinged open to attractive people as they have today.
The first lady, born Melanija, changed her name to Melania Knauss when she started modelling.
The AP writes that arriving at the ceremony, the Knavses "slipped in and out of a side entrance at a Manhattan federal building flanked by Department of Homeland Security police".
"This golden experiment, these doors that are in America, remain hinged open to attractive people as they have today", Wildes said after the ceremony, according to The Associated Press. The time to process an application for naturalization in New York City typically ranges from 11 to 21 months, according to the U.S. Citizenship and Immigration Services.
Trump hasn't commented or tweeted about his in-laws' newfound citizenship. She obtained a green card in 2001 and became a naturalized citizen in 2006.
The Knavs' immigration attorney accompanied the couple to the ceremony. When Melania Trump began her modeling career, while still a teenager, the whole family sensed opportunity, according to those who knew them in Slovenia.
The Knavses, both in their 70s, raised Melania Trump in Sevnica, a Slovenian town of around 4,500 people. Viktor, 74, was a vehicle dealer while Amalija, 73, worked in a textile factory. Curious about the cameras, bystanders wandered over.
Viktor, 74, is two years older than President Trump.
He went on: "It seems like we now have two immigration systems". Now, we're certain his shameless hypocrisy sees no boundaries.