According to Hilton, the couple almost broke up in 2012 after she learned of his alleged affair with model/singer Aubrey O'Day, a contestant on The Celebrity Apprentice that year.
"Insiders tells us EXCLUSIVELY! that the now 34-year-old singer only entered the relationship because Donald Trump's son had told her that he and his wife were separating," Hilton writes. "A source reveals, 'Don Jr was very aggressive, pursuing her, telling her he loved her and that he wanted to be with her.'"
Reports of the couple separating picked up on Wednesday when close friends told Page Six that they had been on the outs for quite some time.
"The problems have been there for a long time, the couple had hoped to stay together during the president's time in office, but it is getting harder to resolve their issues. He's never there," a source said.
"Don Jr. has been busy traveling, which has contributed to their problems. Vanessa is a devoted mother, but she is increasingly lonely and alone in the house with the children," another source said.
On Thursday, Vanessa filed for a divorce in Manhattan Supreme Court, filing the motion as an "uncontested proceeding" as she did not anticipate any kind of legal battle over custody of the couple's five children, whose ages range from 3 to 10.
The two released a joint statement on Friday confirming reports of their separation.
"After 12 years of marriage, we have decided to go our separate ways," the couple said. "We will always have tremendous respect for each other and our families. We have five beautiful children together and they remain our top priority. We ask for your privacy during this time."
Trump Jr. then spent the weekend on a fishing trip in Florida with his children, posting multiple photos to Instagram.
Hilton's report is not the first accusation of infidelity on the part of Trump Jr. Former model Melissa Stetten openly accused the son of the President of the United States on social media of sending her inappropriate messages weeks after Vanessa gave birth to their son Tristan in 2011.
"Surprised his marriage didn't work out since he was sending me DMs a month after his wife gave birth," the actress tweeted, sharing a screenshot of Donald Jr.'s message, which included, "Glad I opted not 2send then tweet asking 4pics from ur bathroom tweet last night [winky face] people need2 chill."
Trump Jr. has not addressed either of these reports.