Article: On 20 September 2013, Queen + Adam Lambert performed at the iHeartRadio Music Festival at the MGM Grand Hotel & Casino in Las Vegas. On 6 March 2014, the band announced on Good Morning America that Queen + Adam Lambert will tour North America in Summer 2014. The band will also tour Australia and New Zealand in August/September 2014. In an interview with Rolling Stone, May and Taylor said that although the tour with Lambert is a limited thing, they are open to him becoming an official member, and cutting new material with him.

Question: When did Queen + Adam Lambert perform at the iHeartRadio Music Festival?
20 September 2013