Olivia Newton-John famously played Sandy in 1978's Grease
Donna Mills
Credit: Donna Mills/Instagram, Paramount/Courtesy Everett Collection

Donna Mills claims to be the blueprint for Grease's Sandy.

The TV icon, who is famous for her Dallas spin-off series Knots Landing, shared a video Sunday in which she dresses up as the character from the 1978 movie musical, a role made famous by Olivia Newton-John. In the clip, Mills said she was the "model" for the character.

"Does the character Sandy from Grease look similar to me? Here's why!" she wrote in the caption.

"Did you know that I went to school with Jim Jacobs?" she said to the camera in the video, referencing the musical's co-writer. Mills added with a laugh that he "used me as his model for Sandy."

"I didn't know it at the time, but I found out years later," she said. "I was the original Sandy."

Jacobs told The Buffalo News back in 2010 how he and co-writer Warren Casey originally came up with the Grease idea, calling it "one of those pipe dreams you have when you're half in the bag at a party."

"We're sitting around in my apartment in like '69, and it was some cast party of a show. Around 1 in the morning, there were still a few old potheads laying around, passed out on the floor," he recalled at the time. "I was sick and tired of listening to Led Zeppelin or whatever the hell I had on the record player, and I dug out some of my old 45s. That's the humble beginnings of it."

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"I was playing Dion and the Belmonts, Little Richard and the Five Satins, and I said to Warren, 'Man, wouldn't that be a gas to do a Broadway show using this kind of music instead of that traditional Brigadoon, Oklahoma stuff that we all know?' " he added.

Grease follows the story of two teens in love in the 1950s — Sandy and Danny Zuko (John Travolta in the movie) — who meet while on summer vacation and reconnect at the start of the school year when Sandy attends Rydell High as a transfer student. The film also starred Jeff Conaway, Stockard Channing, Barry Pearl and Didi Conn.

Mills, who appears in Jordan Peele's upcoming movie Nope, recently told PEOPLE about stepping back from her Hollywood career to become a mom.

"I was very concentrated on my career, but at a certain point, I realized there was something missing — it was a child. So I went after it. I adopted her when she was four days old," she said. "By that time, I was 54 and people said, 'You're going to be so old [to] have a little toddler running around.' I never felt that. I never felt older than the other mothers who were probably in their 20s."

She added, "If you want to give to your career, I say having a child later in life is better than having a child early."