Famous artists or musicians that you were surprised to see in other famous bands?

I found out earlier that after the Stone Temple pilots fired their lead singer in 2013, Linkin park vocalist Chester Bennington joined the band. He was with stp until 2015.

Dimebag Darrell Abbott guitarist of Pantera played the solos for numerous songs on three of Anthraxs albums. Scott Ian guitarist of anthrax called him the "6th member" of the band.

Do you know of any other artists that joined a successful band (or were in famous a band and left to go solo) that surprised you when you first learned about it?