KISS needed to postpone their Salt Lake City show last month so Gene Simmons could undergo surgery to remove painful kidney stones.

According to TMZ, the bassist-singer had a stent inserted into his urethra at Los Angeles’ Cedars-Sinai Hospital on Tuesday to help pass his stones.

Shannon Tweed Simmons, Gene’s wife, shared an update on how he’s doing, posting a photo of the procedure to her Instagram, noting, “Well, now that the cats out of the bag.”

“This is Gene’s second of three procedures that will remove these large kidney stones so he can move on with Rockin’ & Rollin,” she continued, adding, “Happy Anniversary to my wonderful husband @GeneSimmons.”

Ever get a kidney stone? How painful was passing it?

More about: