NASHVILLE, Tenn. — Keith Urban was slyly dropping hints about the surprises he had in store at the All For The Hall benefit concert this week, but little did he know the night's biggest surprise was aimed at him.

Vince Gill and members of Rascal Flatts, The Oak Ridge Boys and Diamond Rio surprised Urban Tuesday night with the announcement he will officially join The Grand Ole Opry this month, a revelation that clearly took the Australian country star by surprise.

"I'm shocked, I've got to say," Urban told the sold-out crowd at Bridgestone Arena. "It's a huge honor and how beautiful to have this happen tonight of all nights."

As for Urban's surprises, he brought Merle Haggard and childhood hero Don Williams on stage, fittingly trotting out a couple of inductees for the fundraiser to benefit the Country Music Hall of Fame & Museum.

"This is one of the biggest thrills of my life, getting to play a little guitar with this guy coming out," Gill said before bringing Haggard on stage.

Haggard played four songs, including crowd favorite "Workin' Man's Blues." Williams, a childhood idol of Urban's, performed two songs, including "Tulsa Time."

"I heard more records in my house growing up by this guy than anybody," Urban told the crowd before bringing Williams on stage.

With the exception of the night's surprise guests, the theme of Urban and Gill's third installment of the benefit was duos, vocal groups and bands.

Urban and Gill served as co-musical directors and house band leaders, sitting in on almost every song and merging their bands for the night.

"Thanks so much to Keith and Vince," Miranda Lambert said. "That's hot!"

Other groups joining Lambert's Pistol Annies on the night's set list included Lady Antebellum, The Band Perry, Thompson Square and Little Big Town. Alabama was the only group not to use the supercharged backing band. Turns out they didn't need them on their somber hits "Lady Down on Love" and "Feels So Right."

"Man, there is nothing like the sound of those voices," Gill said after Alabama wrapped up. "Good Lord!"

Still, little compared with the moment when Gill called all the Opry members in the house back on stage following Rascal Flatts' performance. That trio, also recently invited to join the Opry, brought out a black duffel bag with a surprise inside for Urban. He opened it to find an Opry microphone stand.

Urban appeared to tear up before recovering and addressing the crowd. He also dedicated his invitation to his wife, the actress Nicole Kidman, and his daughters.

"I've been here 20 years this year," Urban said. "1989 was the first year I came over from Australia to take my demo to the record labels. I got a lot of strange looks. ... This night here is in a whole other stratosphere."