Mike and Freddy duets:
State of Shock was written by Randy Hansen and Michael Jackson for his record-breaking 1982 album Thriller, intended as duet with Freddie Mercury. However, as it was not finished in time, it was to be included on The Jacksons' album Victory two years later. Mercury's part was later taken over by Mick Jagger. It was worked on from 1981-83, and a 4:44 demo leaked on July 7th 2002.
There Must Be More to Life Than This (1981-3), written by Mercury, was first considered to be included on Queen 1982 album Hot Space, and two years later on follow-up The Works. In 1983 Jackson sang the song supported by Mercury played the piano, intended for The Jacksons' 1984 LP Victory. As this was also dropped, Mercury went on recording his own version and released it later on solo album Mr. Bad Guy (3:00) in 1985. Jackson's aforementioned 1983 solo demo version, 2:31 in length, was leaked on July 7th 2002. It is not known if they sang the song together; any "leaked" versions online simply merge their voices together from the two completely different recordings.
Victory, the only song they co-wrote, was first considered to be included on Queen's 1982 album Hot Space, then scheduled for The Jacksons' LP of the same name two years later (there is no title track on the album, so its name seemed to remain). The song was not completed early enough, so was eventually dropped. Many years later Queen's remaining members (Brian May and Roger Taylor) worked again on the track, adding some backing vocals, hoping to release it as part of an upcoming Queen box set. This did not materialise due to copyright issues.
May said to Q Magazine in 1988 that all three songs were given away by his mother to two of Michael's fans after contacting her.