Ashlee Simpson Recalls 'Great Moments' Spent with Sister Jessica While Releasing Music in the 2000s (Exclusive)

The singing siblings both released multiple albums throughout the decade

Ashlee Simpson will always be fond of her big sister, Jessica Simpson.

In an exclusive conversation with PEOPLE, the singer and mom of three, 39, reflects on releasing music during the 2000s at the same time as her sibling.

Detailing that she and Jessica, 43, shared "all great memories" together, Ashlee says, "I grew up also touring with her before I went on my own and toured."

"I feel like we've definitely had great moments, and I feel like even when I would do shows, just having her there [was great]," she continues.

"And yeah, all of her outfits, I think mine might've been a little bit more wild than hers," Ashlee — who has partnered with Dairy Queen and the DQ Freezer to bring back some iconic sweet treats — adds playfully.

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During the 2000s, Jessica released her albums Irresistible, In This Skin, A Public Affair and Do You Know, plus her holiday album, ReJoyce: The Christmas Album. Ashlee, meanwhile, released her debut album Autobiography in 2004, before later releasing her LPs I Am Me and Bittersweet World in the years to follow.

Looking back at her first album, Ashlee reflects on what her favorite song was at the time — and what her current favorite is.

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"When the album came out, I would say 'La La' was always super fun to play, and that was one of my favorites," she tells PEOPLE. "It was fun to write that song as well. It was such a fun moment."

"But I also really loved 'Undiscovered.' That was another song that I really liked a lot, and my favorite track now is maybe still 'Undiscovered,' " she adds.

"I go back and I listen, and I'm proud of those moments," continues Ashlee. "It brings me back to just going to the studio every day, coming with what I was going through, and it's kind of being like, there's my diary right there."

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