In a passage from her recently released memoir Unhinged: An Insider’s Account of the Trump White House, the former Apprentice contestant wrote that she first learned about the alleged affair from the former Danity Kane member herself, who was appearing on a season of Celebrity Apprentice at the time.
“Aubrey and I knew each other in L.A., so when she did the show she called me to ask for advice. I next heard from her when she started seeing Don Jr.,” Manigault Newman wrote. “She told me, ‘He’s leaving his wife. They basically aren’t together. They’ve separated.’ ”
While the reality star went on to share that at the time she “didn’t believe that” Don Jr. would ever leave Vanessa Trump, who was pregnant at the time, the next time she met with O’Day, now 34, the singer “showed me very personal photos that Don Jr. had sent to her,” as well as “a long chain of dirty texts between them.”
“If she hadn’t shown me those photos and texts, I wouldn’t have believed it,” the former White House aid wrote.
However, at the time, Manigault Newman decided not to involve herself in the issue.
“I filed their affair under ‘not my business,’ a list that was growing longer every day, but my heart went out to Vanessa,” she wrote. “She was popping out children and holding down the fort in New York while Don Jr. was allegedly running around the world, cheating on her with somebody from work.”
Reps for both Don Jr. and O’Day did not immediately respond to PEOPLE’s requests for comment.
Manigault Newman also wrote in the book that before the alleged affair began, the elder Trump seemingly encouraged his son to cheat on his wife.
“During one boardroom outtake that season, it came out that Donald Trump and Carol Alt had once dated in the nineties. Donald said something like, ‘Yeah, those were the good ole days.’ ” she wrote, adding that he then “turned to Don Jr. and said, ‘You’ve got to get ass like that. You’ve got to get ass like that.’ ”
“I remember being disgusted, thinking, Donald, what are you talking about? Your son is married. His wife is pregnant,” wrote Manigault Newman.
Later on in the book, Manigault Newman wrote that by 2016, when Trump was still campaigning for president, Don Jr. and Vanessa’s marriage was on the rocks.
“I believe that as far back as July 2016, if not even farther, their marriage was hanging by a thread,” she wrote. “But she showed up at the convention and the debates anyway, taking her seat in the row of Trump wives out of respect for her father-in-law.”
RELATED VIDEO: Donald Trump Jr.’s Wife Vanessa Files for Divorce After 12 Years of Marriage
Reports of Trump Jr.’s alleged affair with O’Day began circulating shortly after Page Six broke the news that Vanessa, who shares five children with Don Jr., had filed for divorce after 12 years of marriage.
Although the former pair, both 40, have remained cordial following their split — Vanessa publicly stood up for Don Jr.’s new girlfriend Kimberly Guilfoyle — their divorce was listed as contested in July despite previously being uncontested, according to the Associated Press.
A “contested” divorce means that both parties are not in agreement on all issues. In the Trumps’ case, the issues appear to be financial.
A source who worked with Celebrity Apprentice previously told PEOPLE that Don Jr. and O’Day’s “affair ended” after Vanessa discovered “sexy” text messages between the pair while her husband was in the shower.
While O’Day has not commented on the alleged affair, during a clip from Celebrity Apprentice, the singer wasn’t shy about discussing her feelings, as she confessed that “Don Jr. makes me nervous because his opinion means a lot.”
“He’s done this for a very long time. And also I have a very big crush on him, so I don’t want to disappoint him,” she added.