Kelly Clarkson is finally revealing the secret to her recent weight loss. The pop star opens up about how she managed to slim down.

Coming Clean About Eating Clean

Rumors have been swirling for months about the singer's recent slim-down, but she remained coy about how she did it.

Thursday found Extra publishing an interview with the 36-year-old, during which she confirmed that her weight loss was down to a thyroid condition.

"I literally read this book, and I did it for this autoimmune disease that I had and I had a thyroid issue, and now all my levels are back up. I'm not on medicine anymore because of this book," explained Clarkson in the clip.

The book in question is The Plant Paradox, by cardiac surgeon Steven R. Gundry. The singer explained that she learned all about cooking her food properly, as well as eating organically.

Clarkson also confirmed that working out had nothing to do with her recent slim-down.

"I'm not working out! I think people think I'm working out ... Literally, I haven't worked out at all!" she quipped.

A Noticeable Difference

The singer's weight loss became the subject of much online discussion during the latest season of the reality show The Voice, for which she's part of the judging panel.

Clarkson's svelte figure was evident in a series of glitzy outfits, but when questioned about what had changed, she refused to reveal her secrets.

Following the show's finale last month, she joked that Harry Potter and SPANX were to thank for squeezing her into her tight outfits like sausage meat.

The "Love So Soft" singer also advised that she was having fun experimenting with her style lately, but again credited her glam squad for keeping her looking good, rather than anything else.

Clarkson recently admitted on Twitter that workout clothes sent from country singer, and friend, Carrie Underwood were too big for her. Underwood sent the gift during her activewear line, Calia's, third anniversary. Underwood promised to send some more stuff ASAP.

She Wasn't Happy Skinny

Clarkson made a splash on Wednesday's CMA Awards red carpet too, looking healthy and slim.

The singer revealed that she was very unhappy at her thinnest and didn't want to go back to that difficult time in her life.

 "When I was really skinny and unhappy, I wanted to kill myself. I was miserable, like inside and out, for four years of my life," she told Attitude magazine.

The American Idol winner has been vocal in recent years about the pressure that the hit reality show put her under.

She noted that anybody who minded the weight she gained following her stint in the show should focus on themselves not on her, as she's always been happier with her size.