The Boy Meets World star, 31, revealed the unlikely pairing in a new video blog for PopSugar.com, and admits that she had to ask Bass out on the date.
She says, "When I was a senior in high school I asked my boyfriend at the time if he would go to prom with me, because my boyfriend at the time was Lance Bass. So I had to make sure his schedule would allow for prom.
"Unfortunately he told me no, because he was going to be in Japan (with 'N Sync) and I was so sad.
However, the singer's plans changed and he sent Fishel a large bouquet of roses to make amends for the upset.
She continues, "(He sent) three dozen roses in the mail with a card that said, 'Plans have changed, I'll be in town. Can I take you to prom? Check yes or no.' And there were two little boxes! So, of course, I checked the box yes. And a couple weeks later we were at prom together dancing it up!"
Fishel, who is now engaged to fiance Tim Belusko, also shared a photo of the former couple with fans online. She and Bass dated from 1999 to 2000.