updated 10/10/2011 AT 8:00 AM ET
•originally published 10/10/2011 AT 8:20 AM ET
“I thought she was a 28-year-old heterosexual girl, because that’s what she looked like to me. And she’s a 40-year-old gay woman,” O’Donnell, 49, tells ABC’s Nightline in an interview airing Monday night.
She adds with a laugh: “My gaydar was way off!”