Jillian Michaels, Rachel Frederickson Jillian Michaels, Rachel Frederickson

Biggest Loser trainer Jillian Michaels admits she was shocked when she saw how much weight Season 15 winner Rachel Frederickson had lost.

"I was stunned," Michaels said on HuffPost Live. "Nobody told me like, 'Oh hey, Rachel is very, very thin.' Bob [Harper] and I had no idea. Nobody had told us. Nobody had said anything to us. So yes, I was stunned. Obviously, I thought she had lost too much weight."

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Last month, Frederickson caused a firestorm when she showed off a 155-pound total weight loss on the show's season finale. The 24-year-old former swimmer ultimately weighed in at 105 pounds.

The day after the big win, Frederickson defended her weight loss, claiming she ate 1600 calories a day.  "We are given a calorie budget and I stuck to that," she said. "I followed the advice and support of the medical team at The Biggest Loser the entire journey and I'm going to continue on the path and maintain the healthy lifestyle."

A few weeks later, Frederickson finally expressed in a People interviewthat she was a maybe a "little too enthusiastic" in her training to get to the finale.