For most of her life, Meredith Prince has struggled with her weight and her identity.

The 24-year-old from Rochester, N.Y., was adopted.

"I always knew I was adopted," she said. "They're small and I'm not at all. … I just never felt like I fit into my own [adoptive] family."

RELATED: Chris Powell's Summer Slimdown Tips

After years of yo-yo dieting, Prince, a kindergarten teacher, tipped the scale at 314 pounds.

She reached out to fitness expert and "Extreme Weight Loss" host Chris Powell, and he got her into weight-loss boot camp. Over the course of the year, she pushed herself. She lifted weights, ran and ate well. She even finished a marathon.

"At the heaviest, I was over 400 pounds," Prince said today on "Good Morning America," as she held up an old pair of her jeans in front of her newly slimmed-down frame. "And here we are today at 155 pounds. It's been such a journey."

WATCH: 'Extreme Weight Loss': Chris Powell Helps Obese Twins Get Fitter

Prince's goal weight of 155 pounds meant so much to her, she even had the pledge to the lose weight tattooed on her stomach.

"She actually tattooed her goal on her body. That shows dedication," Powell said. "But one of the most important things we can all do is we need to know where we are going. We need to have that purpose. And sure enough, that's what she did. She got there."

For the first 90 days of her program, Powell asked Prince to lose 80 pounds. She lost 84, and continued to lose weight.

At her final weigh-in, Prince got on the scale and weighed exactly 155 pounds.