Ono, who helped the former BEATLE star write the 1971 song, knew it would be a hit, but didn't expect it to be regularly voted the greatest song of all time.
She says, "When I first heard the finished version of this song I was in a room in Ascot in England with John and my first thoughts were that it would be a hit. The lyrics were just so beautiful.
"We both liked the song a lot but we honestly didn't realise it would turn into the powerful song it has, all over the world. We didn't realise it would be that big.
"We just did it because we believed in the words and it just reflected how we were feeling."