Jessica Simpson shows off her more than 100lb weight loss wearing 14-year-old True Religion jeans

She turns 40 on Friday.

And on Thursday, Jessica Simpson said goodbye to her 30s by showing she could still fit into her 14-year-old True Religion jeans.

The mother-of-three looked strikingly slim in a mirror selfie where she posed in tight distressed denim which showcased her 100lb. weight loss.

The former pop star took the snap in her bedroom at the home she shares with husband Eric Johnson and their kids Maxwell, eight, Ace, seven, and Birdie, 15 months.

Her legs looked ultra-svelte in the frayed blue jeans, which she paired with a trendy tie-dye hoodie. 

In the caption alongside the picture, Jessica wrote: ‘I have kept these throwback True Religion jeans in my closet for 14 yrs (I’m not exaggerating!).

She added: ‘I figured that since I’m in the final hours of my 30’s I’d give them another try, and hello 40, so nice to meet you.’ 

Last September Jessica opened up about her 100lbs weight loss achievement on Instagram.

Along with a chic outfit selfie, she wrote: ‘6 months. 100 pounds down (Yes, I tipped the scales at 240.’

‘My first trip away from #BIRDIEMAE and emotional for many reasons, but so proud to feel like myself again. Even when it felt impossible, I chose to work harder.’

In her memoir Open Book, Jessica revealed how she was pressured to lose weight while in the music industry, recalling one particular interaction with Sony exec Tommy Mottola.

‘On my 17th birthday, I flew to New York for meetings with record labels,” she recalls. “I sang ‘Amazing Grace” for Tommy Mottola at Columbia and he wanted to sign me. And then he said, “You gotta lose 15 pounds.” That’s when the crop-tops came in and the dancing and choreography, and that was all confusing for me.’

‘I immediately went on an extremely strict diet and started taking diet pills which I would do for the next 20 years.’

In the memoir she also reflected on how her role as Daisy Duke affected her body image.

‘[That] created a gold standard Jessica, the “before” for every “is she fat or is she thin” story for the rest of my career. It’s heartbreaking and I mean, I punished myself for it. I heard it and I couldn’t not hear it in the back of my mind every time I was on stage, every time I walked out the door.’

Jessica’s radiated confidence in a June 26 post, where she looked towards her milestone birthday with a bikini photo.

She posed on the beach in a swimsuit and hat in the shot captioned: ‘YEE-HAW to my final days in my 30’s.’

Just a few days ago, on July 5, Jessica and her husband celebrated their sixth wedding anniversary.

They tied the knot in California in 2014 after a four-year engagement.

‘Eric Johnson, my Husband, I love you. 6yrs ago today I married my perfect soulmate,’ the Texas-born star star wrote next to a picture of the couple on Instagram. 

‘Our unity was written in God’s sky of colliding stars. Together we manifest dreams, nurture desire, and hold space,’ she said. ‘Destined, it always has been and always will be, forevermore.’ 

The couple’s anniversary came just days after they celebrated their son Ace’s seventh birthday with a baseball-themed party. 

Eric, 40, a former NFL tight end, is Jessica’s second husband.

In 2002, she had married 98 Degrees boybander Nick Lachey; they divorced in 2006.