In this Sunday, June 4, 2017, handout photo provided by Dave Hogan for One Love Manchester, singer Ariana Grande performs at the One Love Manchester tribute concert in Manchester, north western England, Sunday, June 4, 2017.
Watch video footage of the mistake below, as reported by Digital Spy. He thanked everyone for attending despite a terror attack in London the day before.
During her set, "Part of Me", singer Katy Perry told the crowd: "love conquers fear and love conquers hate, and this love you choose will give you strength and it's our greatest power", before asking the crowd to turn and hug the person next to them.
After all, the performance was being live-streamed across the world so will.i.am could have been addressing London.
Gallagher and Take That hail from Manchester.
All proceeds from the concert went to the We Love Manchester Emergency Fund which was set up by the City Council in partnership with the British Red Cross.
Ariana was joined on stage by 26 students from the Parrs Wood High School choir to sing an emotional rendition of Grande's song My Everything and was visibly moved to tears while performing. "I love you guys so much and I think that the kind of love and unity you're displaying is the kind of medicine that the world really needs right now". "All we feel here tonight is love, resilience, positivity", Williams said before he launched into his hit song, "Happy" with an assist from Miley Cyrus.
She told the Press Association: "We felt we had to unite with London - obviously we have lost our daughter and we felt we needed to come and unite with them and let them know Manchester is supporting them and we are all here for them".
On Friday the 23-year-old singer made a surprise visit to injured fans being treated at the Royal Manchester Children's Hospital.
Towards the end, Grande got emotional as she sang a heartbreaking version of "Somewhere Over the Rainbow" to close out her benefit gig.
"One Love Manchester" airs Sunday, June 4, on ABC and Freeform in the U.S. It'll be live on Freeform at 2 p.m. ET and a one-hour highlight special will air on ABC after the National Basketball Association finals.