The former Hills cast member had ten plastic surgery procedures during one day in 2010, including a nose job, brow lift, ear-pinning, breast implants and a chin reduction.
Montag admitted in a recent interview with Access Hollywood that she got "really excited" about her transformation.
She added: "When you have someone say, 'It's gonna be great', then you really think it's gonna be great.
"My nose was broken so I had to get it re-done, and I was like, 'Well, while I'm there, what else?' And then I kinda wanted a few enhancements and then it got outta hand…
"I should have researched it more and I wasn't really told the repercussions and what would happen emotionally and physically and how much pain I'd be in."
Montag also said that she regretted being interviewed just hours after her surgery, saying that she was "kind of in shock."
"It was really kinda post-trauma; I really was kind of out of it still and recovering," she recalled. "I was very swollen; I probably shouldn't even have been talking at that time… I was kind of not myself."
After her cosmetic surgery, the 26-year-old attempted to launch a pop career, which failed.
She recently said she will keep trying to prove that she is more than her surgeries.
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