Andrew Magnotta | iHeart.com

To be a fly on the wall during the next meeting between Gene Simmons and Paul Stanley would be … uncomfortable.

While Simmons and Stanley’s relationship has generally been characterized as that of “business partners” in KISS, it sure seems like a singer’s waning vocal cords would be off-limits for jokes — being that it affects his career.

Video posted to YouTube by fans who attended one of Simmons’ recent solo concerts in Australia, which featured Ace Frehley, shows the bassist calling “Bulls**t” on his fellow KISS co-founder before bringing some VIP fans on stage to sing “Rock and Roll All Nite.”

“We need some help though; we can’t sing the song by ourselves,” Simmons told the audience, before adding sarcastically. “‘Cause I’m 69 and I’ve lost my voice!”

What’s more, this wasn’t even the only time on this tour that Simmons called out Stanley — who, by the way, had surgery in 2011 to help fix “recurring vocal cord issues.”

“I’ll sing everything,” Simmons said in another video. “Because my voice always works! I don’t lose my voice. I don’t lose my voice…Paul Stanley.”

After a long pause, and some surprised oohs from the crowd, he added, “No, I love him.”

Simmons’ apparent amusement with Stanley’s vocal cords comes off as more than a bit caustic.

While it certainly must be frustrating to be onstage with Stanley when he’s struggling (or singing over vocal tracks), Stanley’s vocal problems aren’t a personality quirk; they’re a medical issue.

Maybe Simmons was annoyed that Stanley insisted earlier this year that he, not Simmons, is KISS’ frontman.

Whatever the reason is, the two better work it out before KISS begins a three-year world tour next year.