The Born This Way hitmaker brought her artRave: The ARTPOP Ball Tour to Tel Aviv, and she shocked fans by bringing her "partner in jazz crime" onstage.
Gaga told the crowd, "Tony surprised me. He just showed up in Tel Aviv, I can't believe it! We're so happy to be here tonight."
The pair performed the standard I Can't Give You Anything But Love from new album Cheek to Cheek, which will be released next week (23Sep14).
Gaga's appearance in Israel came after a number of acts, including the Backstreet Boys, Paul Anka and Neil Young, pulled the plug on scheduled gigs this summer (14), citing security and safety concerns amid the ongoing crisis between Israelis and Palestinians.