Complex sentence: Roy Thomas Baker temporarily reunited with Queen and became their producer; it was three years since he co-produced Queen's 1975 album "A Night at the Opera", but this album also was the last he co-produced for the band.
Split into simpler sentences: Roy Thomas Baker temporarily reunited with Queen and became their producer for this album. It was three years since he co-produced Queen's 1975 album "A Night at the Opera", but this album also was the last he co-produced for the band.