LONDON — Beyoncé Knowles had a little company Tuesday night as she wrapped up her sold-out gigs at London's O2 Arena.

With her concert nearing closing time, Beyoncé was joined on stage by 80's pop star George Michael. Together, the duo performed a duet of Beyoncé's hit No. 1 song, "If I Were a Boy."

Beyoncé returns to the U.S. on June 21 when she performs the first of two shows at New York's Madison Square Garden. The concerts will kick off a North American summer run of her 2009 "I AM..." World Tour, which ends on Aug. 2 after a four-night residency at Encore at Wynn Las Vegas.