Nancy Sinatra has fond memories of working with The King.

The eldest daughter of Frank Sinatra starred alongside Elvis Presley in the 1968 musical action film "Speedway." The singer played a racecar driver while the songstress appeared as his love interest.

"I know he was the funniest man and probably the most serious man I knew, both people in one" Sinatra, now 81, told People magazine on Friday.

Nancy Sinatra Elvis Presley

American singers and actors Nancy Sinatra and Elvis Presley on the set of ‘Speedway,’ directed by Norman Taurog. (Photo by Sunset Boulevard/Corbis via Getty Images)

"He made me laugh so hard," she shared. "And at the same time, he would call me late at night to discuss things like the ghetto and his concern for people in the ghetto. I don’t know if that’s surprising. People who follow his life probably are aware of his sensitivity."

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Sadly, the pair wouldn’t get a chance to collaborate on a different film following the premiere of "Speedway." Presley passed away in 1977 at age 42.

As for Sinatra, she went on to make her mark as an artist. The outlet noted she has 17 albums and several film credits to her name.

Nancy Sinatra Elvis Presley Speedway

Elvis Presley and Nancy Sinatra portray lovers in the musical action flick. (Photo by Michael Ochs Archives/Getty Images)

"[My dad] was very supportive," she said. "There was a time when he went on stage and he’d say, ‘Hello, I’m Nancy’s father,’ because he was so proud of what was happening to me."

The patriarch died in 1998 at age 82.

Back in January, Sinatra opened up to Rolling Stone about what it was really like working with Presley.

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"We were like brother and sister," she told the outlet at the time. "Priscilla was pregnant when we were making the movie, and I gave her a baby shower. He called me the night Lisa Marie was born. And he said he felt that she was so blessed, but that he felt bad that the babies born in the ghetto were not as blessed. He was a very thoughtful, sensitive person."

Nancy Sinatra

Nancy Sinatra is a mother to two daughters. Her second husband Hugh Lambert died of cancer in 1985. ( Photo by Chance Yeh/FilmMagic/Getty Images)

The star also described how she’s always been politically outspoken.

"… I just get so mad," she explained. "In the ‘60s, the Vietnam War was gearing up, and it affected everybody in my life. You had to take a side. I think people are as passionate now as they were in the ‘60s."

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"The Black Lives Matter movement is fabulous," she shared. "And it’s cleansing, because people have to have their voices heard, or you go nuts. If you can’t express your feelings and if you can’t be heard, how awful is that?"