Freddie Mercury and Michael Jackson collaborated on two songs in the early 1980’s that were never commercially released.
One of the tracks was “State Of Shock” which was eventually released as a duet with Mick Jagger replacing Mercury on The Jacksons “Victory” album. Apparently, Jackson and Mercury were too busy with their own tours and albums to get together and finish the song.
The demo of “State Of Shock” with Mercury was leaked to the internet. Here is the demo…
They also worked on the song “There Must Be More to Life Than This” from Freddie Mercury’s solo album “Mr. Bad Guy.” A demo version of Jackson singing and Mercury playing the piano exists, as well as a fanmade remix combining both Jackson and Mercury’s version into a duet.
Here’s the original version of just Jackson on vocals and Mercury on piano.. Mercury eventually released the song without Jackson’s vocals.
This is what Brian May said about the songs and the Jackson/Mercury friendship,
“He (Jackson) used to come see us (Queen) play when we were on tour in the States, and he and Freddie became close friends…close enough to record a couple of tracks together at Michael’s house…tracks which have never seen the light of day”
Here’s a photo of Jackson, Mercury and John Deacon.