Gene Simmons held his latest event for his mammoth Vault collection at the Rio Hotel & Casino in Las Vegas on May 26. And for the first time since he launched the events, his special guest was longtime Kiss partner Paul Stanley.

After entertaining the crowd by himself for a while with stories about his early life and love of music – punctuated with snippets of songs he played on an acoustic guitar – Simmons began jokingly complaining about being forced by Stanley to sing high falsetto parts on songs like "Take Me" and the band's 1979 disco-influenced smash "I Was Made for Lovin' You."

That brought Stanley to the stage for a big hug and a witty rebuke. "You can make fun of 'I Was Made for Lovin' You,'" he said. "Just don't forget I wrote  'God of Thunder,'" Simmons' signature song.

The pair then traded stories about how they first met, and answered fan questions about their songwriting collaborations -- including how their relationship has weathered 49 years of career ups and downs. Along the way, they traded a lot of brotherly jokes about each other and performed impromptu acoustic versions of "Let Me Know," "Let Me Go, Rock 'n' Roll," "Black Diamond," "100,000 Years," "Comin' Home" and others.

You can see a sampling of some of those performances below.

Simmons is holding the "Vault Experience" in cities across the world all year, hand-delivering numbered and limited-edition copies of his Vault box set to fans. The gatherings include listening and Q&A sessions with Simmons, as well as photo opportunities.

So far, he has appeared with former Kiss bandmates Vinnie Vincent, Peter Criss, Ace Frehley and Bruce Kulick, plus current Kiss drummer Eric Singerat stops. All but one of the events has taken place in the U.S. to date; Simmons stopped in London in March. He'll spend several day in Europe and Australia this summer.

Kiss have a light touring calendar this year, with a week's worth of shows in Spain in Portugal in July, with Simmons focusing on the Vault stops and Stanley promoting his artwork. Still, Stanley said Kiss will begin "the biggest tour we've done" at the end of January 2019. There's been speculation that it could be the last shows for the band's current lineup. Earlier this year, they filed a trademark application for the exclusive right to use the phrase "The End of the Road" with regard to live performances, and Stanley has frequently said that they could conceivably continue without him or Simmons, the only two founding members still in the group.

"When a band or anything, a team, lasts 40 years, 50 years, the only way for it to continue is to evolve," Stanley said. "That means in terms of personnel – otherwise, it's impossible. There are bands touring at this point with one or no original members and I have no problem with that, because it didn't happen overnight. It was a series of changes over years or decades. If someone were to say, 'Well, there's no original members in one of the versions of Yes,’ I’d say, 'Who cares?' It sounds like Yes and the pedigree is Yes, so is it Yes? Yes!”