Melissa Joan Hart and Britney Spears shared a big sister-little sister friendship in the '90s, but the actor revealed that she regrets this one thing about it.

In an interview with Entertainment Tonight, Hart revealed that she was the one who took Spears to her very first nightclub at 17 years old.

She shared that she and Spears spent a lot of time together after Hart starred in Spears' 1999 music video for "You Drive Me (Crazy)."

"Britney and I got to do a lot of press together. And we had a lot of fun together during this time," Hart said.

The video became one of Spears' most iconic and was used to promote the film Drive Me Crazy, which starred Hart and Adrian Grenier.

Spears also appeared on Hart's show Sabrina the Teenage Witch as a guest, and clips from the music video were used during the credits of the episode.

READ MORE: Jack Black Covers Britney Spears Song and Sends Her a Message

Hart explained that she viewed Spears as a little sister since she was six years older than the pop star.

"I saw that she was just surrounded by people, never able to break free. And I was like, 'Hey want to come [to the club]?' I would go to a club every night – I love dancing and I loved going out, but I also knew to be responsible and, like, when to stop," Hart shared.

"She was underage and young and – but I [was] just like, 'Let's go out. We're just gonna go out and have some fun.' And yeah – and I feel really guilty about that still to this day because I should have known better, being a big sister," Hart went on.

Hart has six younger sisters and a younger brother.

Spears and Hart briefly reunited during the singer's Las Vegas residency, which ran from 2013 to 2017.

"I saw her when she was doing her Vegas residency a few years back, but she was doing her show so, you know, it was a quick hello backstage and that was it," Hart said.

The two didn't keep in touch after their time working together in the late '90s and early '00s.

Britney Spears in the '90s and Early 2000s

See some of the pop star's most iconic moments and looks from the early days of her career.

Gallery Credit: Ryan Reichard

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