Robin Williams' Real-Life and On-Screen Daughters Team Up on Powerful New Project

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When Zelda Williams stepped out alongside her famous father, Robin Williams, at the premiere of RV in 2006, she didn't know she'd be making a new friend for life.

Pop star JoJo, then 15, starred as Robin's daughter in the film. Ten years later, the actor's real-life and on-screen daughters are not only great friends -- they're working together.

"Her dad always talked about her on set and was like, 'You would love my daughter, Zelda,'" JoJo recalls in an interview with ET. "I was like, 'Dope! I hope I get to meet her.'"

Thinking back on the film's premiere, where the pair was introduced for the first time, JoJo and Zelda can't hold back their giggles.

"It was a very different time for the two of us," Zelda recalls, joking about JoJo's "fancy bandage dress" (Herve Leger, the singer pointedly recalls) and "fake tan."

"It was great," Zelda teases with a big smile.

"Yeah, she had, like, a knife in her back pocket," JoJo quips. "That's my girl!"

WATCH: Zelda Williams Tackles Addiction in Directorial Debut of JoJo's Emotional New Video 

On Friday, JoJo premiered the new video for her heart-wrenching new song, "Save My Soul," and dedicated it to her late father, Joel Levesque, who died in November of 2015. "To me, 'Save My Soul' is about addiction," JoJo explains. "I say it's love and other drugs."

JoJo and Zelda had been looking for a project to collaborate on for years, but were finally able to make it happen when Zelda signed on as director for the video.

"To say the 'Save My Soul' video means a lot to me would be an understatement of stupendous proportions," Zelda said in a statement about the video. "It's not even our shared experiences with addiction and loved ones who suffered from them, though that is the very real inspiration behind this song and video. ... 'Save My Soul' is Jo's very real, very honest ode to addiction, and in her expressing her truth."

"When my father passed, [Zelda] and her mother were one of the first people to reach out to me," JoJo tells ET, looking over at Zelda and fighting back tears. "That meant so much, just because -- I've said this to you many times -- you're a pillar of strength. You were before, and you continue to be. You will always be."

READ: Zelda Williams Pens Hopeful Message About Depression One Year After Robin Williams' Death 

Zelda lost her own father in August of 2014. The actor had publicly faced addiction and, according to a statement from his rep at the time of his death, had "been battling severe depression."

Today, Zelda says fear of falling into addiction herself has never been an issue. "I have an arrhythmia, so I was kind of told really young that -- 'Don't do drugs, you'll die,'" she says.

"I have a lot of family members and friends that went through it. It's not just him [Robin], and I think that's important for a lot of people to know -- it can be anyone," she adds. "That judgment of thinking that it can't happen to you is silly. ... I actually, strangely, have an enormous amount of friends that have made it through the other side of something very difficult. A friend of mine looked to me once, I think shortly after dad died, and said, 'I think it's a little screwed up that you collect broken people.' I remember looking at him and going, 'I think it's a little screwed up that you think people are inherently broken.' I never thought that."

JoJo, however, admits that a fear of addiction can weigh heavy on her mind.

WATCH: On Set With JoJo for Her 'When Love Hurts' Video

"Addiction runs in my blood from all sides," she says. "The roots extend out throughout my family, so I don't think that it couldn't happen to me."

One thing JoJo happily inherited from her father is a love of music.

"My dad and I, our language was music and he was really a free spirit. He could really light up a room," she emotionally recalls. "That's how I'm going to continue my relationship with him is, is through continuing what I love and what we both loved most."

Today, Zelda thinks her own dad would be "proud" to see her directorial debut, while she strives every day to "interact with the world the way he did."

"He didn't care who someone was," she says. "He was always kind. It meant a lot to him, so I hope to, if nothing else, be that."

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