Jessica Simpson shows off 100-lb. weight loss in plunging black dress

Jessica Simpson sheds 100-lbs.

Jessica Simpson shows off new figure in New York City. The mom of three was in the Big Apple for a night of fun and took to Instagram to show off the pounds she lost.

Jessica Simpson flaunted her extreme weight loss while out in New York City.

The singer and entrepreneur, 39, strutted out of her hotel in a curve-hugging black dress with a very deep neckline that exposed her ample cleavage.

"NYC Ladies’ Night," she captioned her photo on Instagram.

Simpson revealed on Tuesday that she lost 100 pounds after giving birth to 6-month-old daughter Birdie Mae in May.

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"6 months. 100 pounds down (Yes, I tipped the scales at 240)," she wrote. "My first trip away from #BIRDIEMAE and emotional for many reasons, but so proud to feel like myself again," the mom of three continued. "Even when it felt impossible, I chose to work harder. "

In May, Simpson returned to working out even though it was difficult for her to get back into a routine.

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"Just stretching it out in my rubber corset. The joy of postpartum," she joked on Instagram.

Back in February, Simpson updated her fans about some health issues she was dealing with while pregnant.

"After a month of sciatica pain, followed by 3 weeks of Bronchitis, I figured since my feet fit in my sneaks today I needed to walk out a lot of anxiety!!" she wrote a the time.

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The singer also dealt with extremely swollen feet for which she underwent cupping treatment and gratefully found some relief.

In addition to Birdie Mae, Simpson and her husband, former NFL player Eric Johnson, 40, share two children together: daughter Maxwell, 7 and son Ace, 6.

In July, she told People magazine that parenting three youngs kids was "no joke."

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"It is definitely constant, and the biggest challenge for me is trying to be present when I am pulled in so many directions,” she continued. “They are all in such different phases now.”

“There is a lot of dividing and conquering going on right now at our house,” Simpson reflected.

Fox News' Mariah Haas contributed to this report.