Montag is claiming the performer sabotaged her music career back in 2010 ahead of her debut album, Superficial.
"People are, like, 'I love Lady Gaga,' and I'm sure she’s great, but I have not had the best encounter with her," The Hills alum revealed earlier this week on “The Unpopular with Jacques Peterson” podcast.
According to the 35-year-old, per Page Six, things between the two took a turn for the worst back when the A Star is Born actress was just an up-and-coming artist.
The ladies were both working with mega-producer RedOne at the time, who Montag claimed said he saw promise in her career, with him going so far as to tell UsWeekly in 2009 of the blonde babe: "She has a star quality — a powerful personality with no limits. She can do anything and make it sound credible. She’s a born star."
Since RedOne, whose real name is Nadir Khayat, and Gaga were writing partners, he needed to first get the musician's permission for Montag to release a track titled "Fashion," given that Gaga wrote it, per the publication. (RedOne and the Grammy Award winner produced several hits together over the years, including “Just Dance,” “Bad Romance,” “Alejandro,” “Judas” and more.)
Montag reportedly claimed Gaga, 35, signed off on the request, responding: "Great, sure, she can have that song."
The wife of Spencer Pratt went on to feature the tune during an appearance on The View, but when producers for the 2009 film Confessions of a Shopaholic expressed interest in the possibility of using the track in the movie, Gaga took the song back form the MTV alum and released it herself, according to Montag.
Montag speculated that Gaga had been a fan of The Hills, as Season 5 of the hit series aired in April of 2009 when their relationship turned sour, and her nemesis Lauren Conrad, which may have contributed to the demise of Montag's blooming career.
Montag recalled one apparent time when the "Shallow" songstress appeared on the reality show and allegedly gushed to the OG cast member about filming with Conrad and Whitney Port.
"I was like, 'Who is this girl? What is happening?' She’s a hater, clearly!" Montag recalled thinking of Gaga, it was reported.
She went on to claim Gaga told RedOne she wouldn't work with him anymore if he was still in business with Montag, leading the mega producer to part ways with the mother-of-one. "He was like, 'I'm sorry, she's my writing partner for huge things,'" Montag remembered of the alleged conversation.
Gaga has yet to respond to Montag's claims.