What a transformation!

Rosamund Pike had her second son, Atom, with partner Robie Uniacke just three months ago — and the 'Gone Girl' star's personal trainer reveals she is well on her way to getting her pre-pregnancy body back.

"She was so fit for 'Gone Girl'. She had never been that fit in her life," Rosamund's personal trainer Holly Lawson said in a new interview.

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Rosamund during her pregnancy (left) and at the Oscars (right) on Feb. 22, 2015. (Photo Credits: Getty Images)

"She really wanted to get back in that space again after having the baby. When she was at the [Golden] Globes we hadn't started working yet, but she had started doing things we did [during filming].

"From the Globes to now is all the work that we put in. She is amazing. Her body is literally back to what it was… she is close to a six-pack again," Lawson continued.

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The 36-year-old actress — who already has two-year-old son, Solo — has slimmed down so much she is already out of her larger clothes, although Lawson doesn't like to focus on any of her clients' weight because she believes being fit and healthy is more important.

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Rosamund at the Golden Globes on Jan. 11, 2015.

"She's back into her pre-baby clothes. I don't go off of weight unless it's required, because I think it can make women, particularly actors, obsessive over something that is not the most important.

"Everything I do and preach is about being the best version of you. Being the strongest, smartest, most loving version of yourself," Lawson told 'E! News.'