Jessica Simpson celebrated sister Ashlee Simpson's 33rd birthday this week.

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The 37-year-old designer dedicated a sweet message to Ashlee on Instagram after ringing in the singer's birthday over the weekend.

"Ashlee- I'm so proud to be your sister," Jessica captioned a photo Tuesday of Ashlee and her kids, 8-year-old son Bronx and 2-year-old daughter Jagger.

"I have always wanted to be as cool as you," she added. "I have never been inspired by anyone more than you! I love you so much! Happy Birthday."

Ashlee shares Bronx with ex-husband Pete Wentz and Jagger with husband Evan Ross, whom she married in 2014.

The singer shared a picture Tuesday of Bronx's homemade birthday gift -- a canvas featuring cute compliments.

"Mom your eyes are like a green forest with a blue lake," the 8-year-old wrote. "Mom your the best mom and theres billions moms you should know that! Happy birthday I love you so much!"

Entertainment Tonight reported Ashlee celebrated her birthday with Evan, Jessica and the designer's husband, Eric Johnson, Saturday at Beauty & Essex in Los Angeles.

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Jessica presented her sister with a Gucci-themed birthday cake.

"She was over the moon!" a source said of Ashlee.

"Evan never left Ashlee's side," another insider added. "She was snuggling up for her husband all night long."

Ashlee released the album Bittersweet World in 2008, and has since starred in "Chicago" on Broadway.