The Bad Romance hitmaker has been gigging Down Under on her own tour this month (Aug14) and during her night off, she treated Queen fans by duetting with the rockers and Adam Lambert, who is fronting the band for a worldwide trek.
Gaga wore a voluminous black wig and a ripped jumpsuit as she strutted around onstage at the Allphones Arena in Sydney and sang Another One Bites the Dust with Lambert.
Following the surprise appearance, Gaga wrote on Twitter.com, "I just played with Queen, I'm the happiest girl alive! #Qal (Queen and Adam Lambert)," while guitarist Brian May adds, "Thanks Sydney for a great night ! And thanks to our great and lovely pal Lady Gaga."
Gaga's Australian trek finishes on 31 August (14), while The Queen + Adam Lambert tour will conclude in Auckland, New Zealand on 4 September (14).