She called her a blonde goddess, and felt she couldn't compare physically, according to her friend Cynthia McFadden.
When it came to booking the best guests for her infamous interviews, Barbara Walters had an incomparable tenacity. So when ABC News hired Diane Sawyer in 1989 to do essentially the same thing she was doing, Walters got highly competitive.
"If somebody gets the interview before me and I didn't try, I'll be mad at myself. I'll think, 'Why didn't I, why didn't I make one more phone call?'" Walters once told Johnny Carson.
In the upcoming documentary Barbara Walters: Tell Me Everything, director Jackie Jesko explores Walters' incredible life and career, including how she felt about Sawyer.
"Barbara did not know why Diane was hired to start a new news magazine within our home of ABC to compete with 20/20," former 20/20 executive producer Victor Neufeld says in the film. "Barbara was unhappy."
While she was, of course, competitive when it came to booking the best guests, friends, and colleagues, she was also intimidated by Sawyer's looks, especially as she never believed she was very pretty.
"She used the word blonde goddess," her friend Cynthia McFadden says in the film, of how Walters referred to Sawyer.
McFadden tells PEOPLE that Walters could be "painfully insecure."
"She thought Diane was the ideal woman, and she couldn't compete with that. She could work harder. She could know more people. But she couldn't compete with the blonde goddess," she says.
20/20 producer Martin Clancy also notes in the film, "Barbara watched Diane warily, because she was really in the same altitude as Barbara. Other correspondents were not a threat. I think Barbara secretly resented Diane for being younger."
Much of the documentary explores Walters' insecurities, which plagued her despite her incredible accomplishments. Part of that stemmed from the hurdles and abject sexism she faced from the very start of her career.
After regularly appearing on TV beginning in 1964, Walters broke her first barrier a decade later when she became the first female cohost of NBC's Today show. In 1976, ABC hired her as the network's first female nightly news co-anchor, opposite Harry Reasoner.
But the men in the old boys' club hated sharing the spotlight with a woman. "Harry was downright rude to her," says McFadden.
The film shows other male colleagues icing her out. "I would walk into that studio, and Harry would be sitting with the stagehands, and they'd all crack jokes and ignore me. No one would talk to me. There was not a woman on the staff," Walters recalls in resurfaced commentary in the film, adding that she felt "bullied," and calling it "the most painful period in my life."
Still, her career undoubtedly paved the way for other women in news, including Sawyer. Despite the tension between the two behind the scenes, Walters once told Charlie Gibson that there was no feud between them, but they were just trying to get the same people for exclusive interviews.
"I don't think Diane Sawyer and I had a feud," Walters said. "I think people know that we were after the same gets."
Barbara Walters: Tell Me Everything, which is produced by Brian Grazer and Ron Howard's Imagine Documentaries for ABC News Studios, begins streaming June 23 on Hulu.