Ariana Grande may be just 23 years old, but she showed the poise, strength and guile of someone 20 years her senior at Sunday's One Love Manchester benefit concert at the Emirates Old Trafford cricket grounds in Manchester.
"What an incredible thing we're doing tonight, would you agree", Bieber said.
"Last night, this nation was challenged and all of you were challenged, and you had a decision to make if you were going to come out here tonight", he said. "And this evening has been so light and so filled with fun and love and bright energy, and I want to thank you for that".
Grande announced the show last week on social media, writing that she had been thinking of her fans "nonstop" and planned to return to the city to spend time with her fans, known as Arianators, there.
He added: "As unfortunately we saw yesterday, this will test us, and will show its face again". Seven civilians died in the Saturday night attack, after a van screeched onto the sidewalk on London Bridge, slamming into pedestrians, before three assailants ran into a nearby open-air market area wielding large knives.
During the show Grande duetted with Miley Cyrus on Crowded House's Don't Dream It's Over and was joined on stage by her boyfriend Mac Miller as they performed their collaboration The Way and Miller's track Dang!
An emotional Grande, who mostly kept it more about the music, did have a brief comment for the audience when she thanked everyone for "coming together and being so loving and strong and unified".
Perry also left a mark with her resilient performance: She sang a stripped down version of her hit, "Part of Me".
Her oversized white sweatshirt reads "One Love Manchester" in graffiti writing, and provided the comfort we're sure she needed on this hard night. We choose to love our families, our friends, and our country.
A third fan said that today's concert would be "really emotional".
"Manchester, I love you with all of my heart", Grande said before the performance, and just after singing "One Last Time" with Miley Cyrus, Pharrell and more of the show's performers standing behind her in solidarity.
Mrs Brownbill and daughter Hannah, 13, said they felt they had to attend to "support the people who weren't so lucky as us". Disney's young adult cable network Freeform will air the full concert live.