David Guetta's song, "Titanium" has been a world-wide hit! It was certified double platinum by the Recording Industry Association of America  and as of March 2014, the song has sold 3,852,000 copies in the U.S.

But did you know that the song originally featured the vocals from Mary J. Blige? Sia recorded a demo of herself doing the song, which was then sent to Blige and other artists. But Eventually, Guetta decided to use Sia's version and the rest is history.

Here is Mary J. Blige verson. What do you think?