Jessica Simpson has shown off her weight loss in a plunging bathing suit.

The 34-year-old singer has been working hard to regain her slim figure following the birth of her 14-month-old son Ace.

And now the Weight Watchers spokeswoman has stripped off to a black one-piece to display the results in all their glory.

In the picture, Jessica is seen proudly showing off her tiny waist, muscular legs and toned arms in the swimming costume.

Posting the picture on her Instagram page, Jessica wrote: “Oh yea girl...We are proud to be in our bathing suits!! @baylormcg #hardworkpaysoff #workoutpartnersforlife.”

The summery snap was taken at Jessica’s sister Ashlee’s bridal shower in Hawaii, ahead of her wedding to Diana Ross’ son Evan.

Another picture of all the girls celebrating the occasion was posted on Instagram, with Jessica writing: "All the beauties celebrating @ashleesimpsonofficial / @missbananahammock!!! I love you Ash. :)"

Jessica’s bathing suit snap isn’t the first time she has stripped off to show the results of her diet.

According to reports the star, who has been a spokesperson for Weight Watchers since 2012, has already dropped 50lbs since the birth of Ace, but is keen to lose even more weight.

However, friends of the star are said to be concerned that she is taking her quest for the perfect figure too far.

“She's become an exercise addict,' a source told In Touch Weekly magazine. “She walks six miles a day, strength-trains three times a week and constantly runs on a treadmill. She's gotten so carried away, she's fainted on a few occasions.”

Jessica is also mother to two-year-old daughter Maxwell with husband Eric Johnson.

The pair married in California on July 5.

The nuptials took place at the San Ysidro Ranch and 275 of the couple’s friends and family were invited. Jessica walked down the aisle wearing a Carolina Herrera strapless champagne and gold gown with tulle layers.