Hard to believe that these two photos were taken in the same month, right?

Holly Madison gave birth to her daughter Rainbow Aurora Rotelle on March 5 -- but, looking at her just three weeks later, it's hard to tell she was ever pregnant in the first place.

The former "Girls Next Door" star hit the red carpet on Friday night for the "One Night for One Drop" World Water Day event in Las Vegas to show off her post-baby bod in a belted, electric blue dress.

And doesn't she look great?

While Madison's belly ballooned during her pregnancy, she didn't really gain weight anywhere else ... so the Before & After isn't too surprising.
And though she looks great now, Holly tells In Touch she's planning on getting back to her pre-baby weight of 110 pounds in the next month.

"We’re putting a gym in our house, so I’ll be doing yoga, Pilates and cardio," she told the mag of her weight loss plans.

See how other celebs have dropped the baby weight in the gallery above!

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