The 'No Matter What' hitmakers thought the quintet were ''a laugh'' but admit their raucous ways left the Irishmen feeling nervous around them.
Boyzone's Shane Lynch exclusively told BANG Showbiz: ''They've always been a great bunch of girls, during the 'Live & Kicking' days, the TV shows we used to do together - they were always the loudest band down the corridor in the BBC studios.
''They were a laugh and had a lot of great, fun times. We were Irish and quiet and young, a little bit naïve and innocent and these five head bangers were loud and fabulous and beautiful.
''They were in a different world, they were quite scary to us, that's probably why we more intimated by them than anyone else.''
Spice Girl Mel C sang with Shane and his bandmates Ronan Keating, Keith Duffy and Mikey Graham on a TV special earlier this month and the group were delighted to have her on the show.
Shane, 37, added: ''We never had the pleasure of working directly with each other [Spice Girls], we did many shows together back in the nineties on the same bill but we never actually sang together. Mel C was more than delighted to be asked.
''She was brilliant and we all reminisced on the show about good times and travelling through Europe together when they had the Spice bus.
''It was great to have someone singing and sitting next to you who has been through the same 20 year period. She's such a beautiful girl too, an absolute lady.
''Each of the individual girls has all stepped into other roles, TV, [fashion], and it's great to see that sort of success. That's one of the things that as a band, we were able to do as well, we're of the same kind of calibre.''
He also slapped a jet-lagged Taylor Hawkins.
The acclaimed performer had just cancelled touring due to a battle with cancer.