R&B superstar Beyonce was sick when she recorded the vocals for her popular song Xo.

The Halo hitmaker reveals the version of the mid-tempo ballad fans have fallen in love with wasn't intended for inclusion on the final cut of her recent self-titled album, because she wasn't pitch perfect during the studio session.

She tells Out magazine, "When I recorded Xo I was sick with a bad sinus infection. I recorded it in a few minutes just as a demo and decided to keep the vocals."

But Beyonce admits Xo isn't the only track that features rough cuts of her singing: "I lived with most of the songs for a year and never re-recorded the demo vocals. I really loved the imperfections, so I kept the original demos. I spent the time I'd normally spend on backgrounds and vocal production on getting the music perfect."