I think maybe you misunderstood. At some point recently it came to David Gilmours attention that he and Roger Waters both support the same charity (the Hoping Foundation) Apparently this occurred without either one of them knowing that the other was also involved in the charity. Once Gilmour found out that Roger also supported the Hoping Foundation, David saw this as an opportunity to mend some fences, and help the cause. With a scheduled performance upcoming in support of the charity, Gilmour decided to ask Roger if he would appear at the fundraiser on stage with him. Roger was thrilled at the idea of performing some Pink Floyd classics with David again. Roger however had an issue with one of the non Floyd songs that Gilmour wanted the two of them to perform. Roger felt the song was too far out of his vocal range and didn't want to embarrass himself on stage. Gilmour attempted several times to convince Roger that he should perform this song with him. Finally Roger agreed to do the song upon one condition, that David join him onstage at one of his upcoming tour dates to perform one song. Gilmour agreed and the charity performance with both he and Roger happened. Now Gilmour is committed to performing at one of Rogers upcoming "The Wall" tour dates.
