NEW YORK (AP) — After three decades of keeping mum, Barbara Walters now says she had a past affair with married U.S. Senator Edward Brooke, whom she remembers as "exciting" and "brilliant."

Appearing on "The Oprah Winfrey Show" scheduled to air Tuesday, Walters shares details of her relationship with Brooke that lasted several years in the 1970s, according to a transcript of the show provided to The Associated Press.

A moderate Republican from Massachusetts who took office in 1967, Brooke was the first African-American to be popularly elected to the Senate. Both he and Walters knew that public knowledge of their affair could have ruined his career as well as hers, Walters says.

At the time, the twice-divorced Walters was a rising star in TV news and co-host of NBC's "Today" show, but would soon jump to ABC News, where she has enjoyed unrivaled success. Her affair with Brooke, which never before came to light, had ended before he lost his bid for a third term in 1978.

Brooke later divorced, and has since remarried. Calls to a listing for Brooke in Miami by The Associated Press were not immediately returned Thursday.

Walters is the guest of Oprah Winfrey to discuss her new memoir, "Audition," which covers her long career in television, as well as her off-camera life. On "Oprah," Walters recounts a phone call from a friend who urged her to stop seeing Brooke.

"He said, 'This is going to come out. This is going to ruin your career,'" then reminded her that Brooke was up for re-election a year later. "'This is going to ruin him. You've got to break this off.'"

Winfrey asks Walters if she was in love.

"I was certainly — I don't know — I was certainly infatuated."

"Infatuated."

"I was certainly involved," Walters says. "He was exciting. He was brilliant. It was exciting times in Washington."

Also during the program, Walters chokes up while describing the struggles of her older sister Jackie, who was mentally retarded. Walters confesses that, as a child, she sometimes felt embarrassed by Jackie.

"She stuttered terribly. People made fun of her. People made fun of me," Walters says. "I didn't bring friends home. I felt terribly guilty because she was very loving and I didn't always feel that way."

Jackie Walters died in 1985 of ovarian cancer.

"When I think of her, because she was beautiful and loving and all of that, it makes me cry."

Brooke served two full terms from 1967 to 1979, taking on the populist causes of low-income housing, increasing the minimum wage and mass transit. He received the Presidential Medal of Freedom in 2004, an honor only 21 U.S. senators have received.