Whitney Houston sings the national anthem at the 1991 Super Bowl. (George Rose/Getty Images)

By Chris Cuomo and Andrew Paparella

It was what turned a star into a superstar: Whitney Houston's mesmerizing rendition of the national anthem at the 1991 Super Bowl. Houston's powerful "Star Spangled Banner" performance came at a poignant, patriotic time - the U.S. had just entered the 1991 Gulf War .

But here's what you didn't know: What the Super Bowl audience and hundreds of millions of TV viewers heard was lip-synched.

"The music was pre-recorded, and so was the vocal," confirmed Rickey Minor, who was Houston's musical director at the time.

Minor, now the band leader on Jay Leno's "Tonight Show," said that in a crowd that large and loud, it was impossible for Houston to hear herself. Though she did sing, it was her pre-recorded voice that the audience heard.

Here's another surprise: Minor and Houston changed the national anthem to ensure a better performance.

"The original version is in 3/4 time, which is more like a waltz," Minor explained. "What we tried to do was to put it in 4/4 meter… We wanted to give her a chance to phrase it in such a way that she would be able to take her time and really express the meaning."

Minor was nervous that the altered anthem wouldn't be well received, but that story, at least, has a happy ending: Houston's performance electrified the stadium and soon after, popular demand prompted Houston's record label to release a single that hit the top 20 on the Billboard charts.

"I think it might well be the best Super Bowl performance of all time, " said Billboard Magazine editor Danyel Smith. "It may well be, with the exception of her version of Dolly Parton's, 'I Will Always Love You,' the most remembered thing about her. I think our grandkids will look at the video for 'I Will Always Love You' and they will look at the video of Whitney Houston singing at Super Bowl twenty-five."

Watch the full story on "One Moment in Time: The Life of Whitney Houston," a two-hour "20/20? special Friday at 9 p.m. ET.