Jessica Simpson Marks the End of Her Thirties by Getting Back Into Her 14-Year-Old Jeans

Jessica Simpson is ready for 40!

Simpson, 39, will be ringing in her next decade on Friday and commemorated the milestone by trying on some vintage jeans from her twenties.

"I have kept these throwback True Religion jeans in my closet for 14 yrs (I’m not exaggerating!)," Simpson wrote on Instagram, sharing a mirror selfie of herself rocking the denim, which she paired with a black and purple sweatshirt.

"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," the mother of three added.

Last month, the singer and actress said "YEE-HAW" to the "final days" of her 30s by donning a cowhide-print bikini and embellished black hat as she posed for a photo on the beach.

RELATED: Jessica Simpson Celebrates 'Perfect Soulmate' Eric Johnson on Their 6th Wedding Anniversary

The author celebrated another major milestone this week -- her wedding anniversary with husband  Eric Johnson.

The couple rang in six years together on Sunday night, and Simpson shared a sweet tribute to the former NFL player on Instagram, saying that she married her "perfect soulmate."

"Eric Johnson, my Husband, I love you. 6yrs ago today I married my perfect soulmate," she wrote. "Our unity was written in God’s sky of colliding stars. Together we manifest dreams, nurture desire, and hold space. Destined, it always has been and always will be, forevermore."

She added that a crystal butterfly from Johnson was her "dream gift."

RELATED: Jessica Simpson Posts Cheeky Bikini Photo Ahead of 40th Birthday: 'Final Days in My 30s'

She concluded the post with a quote from Emily Brontë's Wuthering Heights: "Whatever our souls are made of, his and mine are the same."

Simpson and Johnson share three children, Maxwell Drew, 8, Ace Knute, 7, and Birdie Mae, 15 months.

The pair tied the knot in a lavish wedding celebration in 2014 at the San Ysidro Ranch in Montecito, California, and celebrated the 10-year anniversary of the day they met in May.

Earlier this year, Simpson released her memoir, Open Book, in which she opened up about her relationship with John Mayer, her marriage to Nick Lachey, her struggles with drinking, and plenty more bombshells.