Justin Bieber joined Ariana Grande for a surprise performance on Sunday during her Coachella headlining set

It may be too late for Morgan Stewart to say “sorry” to Justin Bieber.

Earlier this week, E!’s Nightly Pop host slammed Bieber, 25, for his Coachella performance on Sunday, in which the pop star joined Ariana Grande on stage and was caught lip-syncing to his hit song “Sorry.”

“I did not realize it was going to be that bad,” Stewart said on the show before ripping into Bieber’s facial appearance. “He definitely looks like he put an Oxy pad on that forehead, but I don’t care. That is f—ed up!”

On Wednesday, Bieber caught wind of her negative comments and in a lengthy thread on Twitter, the singer addressed the former Rich Kids of Beverly Hills star, whom he compared to a bully at school, and defended himself over the Coachella lip-sync controversy.

“@Morgan_Stewart just saw a video of you ripping me to shreds saying I was lip-syncing. They played the song and i just sang overtop of it,” Bieber explained in his first tweet. “regardless why spend your time tearing people down. It’s people like you that are bullies at school that are making kids suicidal.”

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JUSTIN BIEBER/TWITTER

The singer, whose surprise performance marked the first time he was on stage in two years, then continued his argument and slammed Stewart for “belittling people” and hurting others.

“imagine if you spent even half the time you spend laughing at other peoples expense actually building people up and encouraging people how much positivity you could bring,” he wrote. “What hurts about this is the fact that you have a platform to make a difference”

“And rather than being positive you belittle people. Think about how awesome it felt for me to be on that stage after being away for so long the excitement and joy it gave me doing the thing i love the most, i sang to to backtrack like most cameos do this is a normal thing [sic],” he continued.

“And rather than try and make people feel accepted and loved you find things to pick apart like the world isn’t full of that already.. we can find something negative to say about anything or anyone”

In a final note, Bieber asked, “When are we gonna be the kind of people that find joy in adding value to one another and not tearing each other apart..”

Bieber wasn’t the only one to slam Stewart for her comments. Immediately after posting his tweets, Grande also came to her friend’s defense.

In a series of since-deleted tweets, the “thank u, next” singer, 25, defended Bieber for lip-syncing, explaining that their decision to perform together was not planned, which caused him to rely on the backtrack.

“we also decided to do this ten minutes before my set started. we had 0 soundcheck, 0 rehearsal,” Grande tweeted. “u were singing with the back tracking like most cameos do. people are bored. people don’t know how it feels to be under such scrutiny. the world was happy to have u on stage again.”

She added in a separate tweet: “i don’t like when people try to ruin beautiful moments for my friends that’s all. have a good day.”

Grande also responded to a clip of Stewart’s comments on Nightly Pop, which was shared by a fan, and explained that in her perspective, kindness was far more important than someone’s appearance.

“people look so ugly when they talk about other people like this, it’s crazy. like no matter how pretty you are or how long u spent getting ready, u ugly to me now,” she wrote in the tweet, before asking, “HOW do people watch s— like this lmao.”

Representatives for both E! and Stewart did not immediately respond to PEOPLE’s request for comment.

Justin Bieber and Ariana Grande. KEVIN MAZUR/GETTY IMAGES FOR AG

One week after Bieber was first spotted at the annual music festival, he took to the stage with Grande during the end of weekend two.

“We thought it might be fun to do something for you guys,” Grande said before the pair, who are both on Lil Dicky’s new single “Earth,” performed his 2015 hit.

“I haven’t been on stage in like two years. I came out here I had no idea I was going to be on stage tonight,” Bieber told the crowd. “So anyways this is my first time on stage in two years. I had to get my groove back, my swag back. By the way — album coming soon.”

Following the performance, Bieber went on to share that returning to the stage “felt right,” as he thanked Grande, and his fans, for all their support. “Thank you @ArianaGrande . Thank you @coachella. That felt right. Love you,” he tweeted.

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