"Originally it was due to be with Katy Perry who was really at the top of her game," Spike revealed.
"[But] it turned out that she couldn't rehearse because her schedule didn't allow her to get in with enough time to rehearse anything with Brian May."
"[And] Roger Taylor quite rightly said 'No rehearsals, no gig, we wouldn't do that."
According to Spike, Katy's agent then threw Adam's name into the mix for consideration.
"The manager of Katy Perry said, 'Oh I've got this other artist, Adam Lambert, would you consider using him?"
"So they took the chance...He came into rehearsals, I mean having learned our lesson from Live Aid, we knocked over an 11-minute medley which went on and obliterated everybody else."
The keyboardist then went on to add that it wasn't the first time he, and fellow Queen band members had seen something special in Adam, after seeing the powerhouse vocalist perform Bohemian Rhapsody on American Idol.
"I was very pleased that there was someone out there that you could think about, even consider singing this stuff."
Queen + Adam Lambert last toured Australia with their 'Rhapsody' Tour in February 2020. They are currently touring Northern America.