Brian May and Roger Taylor performed together at several award ceremonies and charity concerts, sharing vocals with various guest singers. During this time, they were billed as Queen + followed by the guest singer's name. In 1998, the duo appeared at Luciano Pavarotti's benefit concert with May performing "Too Much Love Will Kill You" with Pavarotti, later playing "Radio Ga Ga", "We Will Rock You", and "We Are the Champions" with Zucchero. They again attended and performed at Pavarotti's benefit concert in Modena, Italy in May 2003. Several of the guest singers recorded new versions of Queen's hits under the Queen + name, such as Robbie Williams providing vocals for "We Are the Champions" for the soundtrack of A Knight's Tale (2001).

Which two members of Queen performed together at several charity concerts?