Def Leppard go back 16 years with Taylor Swift, having collaborated with her in 2008 on CMT Crossroads before she became the dominant artist she is now.
In an interview with the Los Angeles Times, Leppard singer Joe Elliott says, "I don't think anybody could [see how big she would become]. You look at it now and it kind of makes sense. But if you think back to 2008, there was no such thing as what she's accomplished.
"I know anybody that was there when The Beatles and The Rolling Stones came over will go, 'Wait a minute…' But for people born this century or in the '90s, this is a phenomenon that's never been seen before -- technically bigger than The Beatles and The Stones combined, at least commercially.
"It's insanity, the amount of tickets she sells. But I always knew she'd be big. And for all the hardships she's gone though -- the people who've tried to trip her up over the years at certain parts of her career -- she's just dusted herself down. She's a fantastic role model for a generation of kids."
Elliott recently saw Taylor, having taken his eight-year-old daughter to a show in Dublin, where he lives. "It was a very magical moment. I will forever be grateful to Taylor for making Daddy look cool for a couple of days."