The Nothing Compares 2 U hitmaker claims Gallagher was at the event with his former band Oasis and got so caught up in the festivities, he proposed to her - but O'Connor is the only one who remembers the encounter.
The Irish singer made the revelation in the new issue of the U.K.'s Uncut magazine after answering a question submitted by Noel's estranged brother Liam.
The Beady Eye frontman asked, "You've always been effortlessly cool. How do you manage that?", to which O'Connor replied, "Oh, that's sweet. I've never seen myself as cool, but I'm flattered. Actually, Liam's brother Noel once asked me to marry him, just before he married Meg Mathews. He won't remember, as he was off his face (drunk) at a festival in Amsterdam."
Gallagher wed his first wife Mathews in June, 1997.
During the Uncut interview, O'Connor also called on her old pals to put their differences behind them and reunite for the sake of their mum, Peggy - because she would be heartbroken if her kids refused to talk to one another.
She said, "I am so glad to hear from Liam because I, as a mammy, am not happy that him and his brother aren't getting along well, and their poor mammy must be very upset. Tell Liam I love him and his brother and I'd like them to get on with each other. Do it for mammy's sake, yer feckers (sic)!"