Trump boasted of having the "direct number" to her ex-husband at the White House, telling ABC News she talks to the President about once every 14 days.
"I have the direct number to White House but I don't really want to call him there because Melania is there and I don't really want to cause any kind of jealousy or something like that because I'm basically first Trump wife, OK? I'm first lady, OK?" she told ABC, laughing.
The current and only first lady fired back via a sharply-worded statement to CNN from her communications director, Stephanie Grisham.
"Mrs. Trump has made the White House a home for Barron and the President. She loves living in Washington, DC, and is honored by her role as first lady of the United States. She plans to use her title and role to help children, not sell books," Grisham said, adding, "There is clearly no substance to this statement from an ex, this is unfortunately only attention-seeking and self-serving noise."
The statement is a stunning departure for Melania Trump, who, until Monday, had largely stayed above the fray, isolating herself from negativity and critics.
She has refrained from wading into news-of-day debates and controversy, focusing on son Barron, 11, and working to develop her platform as first lady. When her husband's ex-wife's book comes out on Tuesday, she will be traveling to West Virginia, where she will visit with infants affected by opioid addiction.
Though the first lady has previously said
she has a "thick skin" and isn't bothered by criticism, it is clear that Ivana Trump's comments struck a nerve.
Ivana and Donald couple divorced
in 1992 following his tabloid affair with Marla Maples.
Ivana Trump, who is the mother of the President's three eldest children, Donald Jr., Ivanka, and Eric, does not refer to the President's second wife, Marla Maples, by name in the new book, which comes out Tuesday, only calling her "showgirl."
"Donald during the divorce was brutal. He took the divorce as a business deal and he cannot lose, he has to win," Trump said, adding that they are now "friends."
Daughter Ivanka Trump has said her parents take a similar "all out" approach to life. Her mother's comments to ABC reflect a similar -- if provocative -- tact to the unfiltered rhetoric that made Trump's candidacy successful.
"My mother is an exuberant woman, filled with a passion for life and adventure that made it hard for her to stay in one place for long," daughter Ivanka Trump wrote in her 2009 book, "The Trump Card." "My parents are strikingly similar in that regard. They've grown apart, and even when they were together they seemed to be cut in different ways, but they do share an approach to life: all out, all the time."
Trump also weighed in on a number of hot-button issues during the interview.
She said she had "zero concerns" about Justice Department special counsel Robert Mueller's investigation into Russian interference in the 2016 election, including as it pertains to her eldest son, Don Jr., who has been called to testify.
"I know that he was not involved at all in any wrongdoing," she said.
She declined to talk about the 2005 "Access Hollywood" tape
, saying, "I don't want to go into it." Asked whether she ever talked to the President about it, she said, "Not really, no."
Trump, who was raised in Czechoslovakia, also discussed immigration.
"I'm (an) immigrant myself and Donald is building the wall. I don't mind immigrants and the wall because you have to protect your borders," she said.
Pressed on whether she agreed with the President's policy on ending the Deferred Action for Childhood Arrivals program, she said, "I really don't know, I would not send (away) probably thousands and thousands of kids which were born here. But it's very political and very confusing. So I really don't have an answer on that."
Trump, who claims "full credit" for raising her three children with the then-businessman in her book, also said her ex-husband was a "loving father" but was not involved in their day-to-day upbringing.
"Donald was on the telephone making the deals," she said. "He was loving father, don't get me wrong. And he was a good provider. But he was not a father which would take a stroll and go to Central Park or go play baseball with them. It was only until they were about 18 years old he could communicate with them, because he could talk business with them."
CORRECTION: A photo caption for this story has been corrected to properly identify first lady Melania Trump and President Donald Trump's first wife Ivana Trump.