The parents of U.S. first lady Melania Trump, Viktor and Amalija Knavs, await the start of the official arrival ceremony held by U.S. President Donald Trump and Mrs. Trump for French President Emmanuel Macron and his wife Brigitte Macron on the South Lawn of the White House in Washington, U.S., April 24, 2018.

The parents of first lady Melania Trump became naturalized U.S. citizens on Thursday, taking the oath in a private ceremony in New York, according to their attorney.

Viktor and Amalija Knavs are originally from Slovenia but have lived in the United States for over a decade, during which time they gained permanent legal residency, said Michael Wildes, the couple's immigration lawyer.

Wildes told reporters the couple "have travailed a wonderful journey like millions have, in getting citizenship and waiting the requisite period of time."

He said that despite having the president of the United States for a son-in-law, the Knavses followed a process to gain their citizenship that "was no different than anybody else's."

The White House declined to comment on the Knavses' newly acquired citizenship status, saying they were "not part of the administration and deserve privacy."

After living between Trump Tower and Mar-a-Lago for several years, Viktor and Amalija Knavs reportedly moved to the Washington suburbs following Trump's inauguration,and are frequently spotted traveling with the first lady and the Trumps' son, Barron Trump.

The question of how the Knavses originally gained their green cards has become a controversial one since Trump won the presidency on an anti-immigration platform. Trump has frequently railed against the family visa system, or so-called chain migration, which permits U.S. citizens to sponsor their family members for visas.

Even so, experts say chain migration is the most likely way the Knavses gained their permanent residency in the United States.