Shawn Mendes apologised for misgendering Sam Smith.
Sam come out as non-binary in September last year and now uses pronouns they/them.
Shawn, 22, introduced the super star, 28, with the masculine pronoun "he" during Thursday's iHeartRadio festive special.
In an apology, the singer admitted the pronouns had "absolutely slipped my mind".
He wrote: "Oh @SamSmith I'm so sorry for referring to you as a "he" for your jingle ball introduction.
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"It absolutely slipped my mind. Won't happen again. Sending you so much love!
"Also you absolutely are one of the funniest people I've ever met."
Sam accepted the apology and shared it with their own fans on social media.
They responded: "We're all learning together. Happy holidays, all my love xx."
Shawn gave Sam a warm welcome by describing the star as one of the "sweetest, kindest and funniest people".
During his introduction, the Señorita hitmaker accidentally made the slip up over pronouns on iHeartradio.
Later, he was quick to apologise to Sam.
Initially Shawn had said: "I'm super excited to announce the next iHeartRadio Jingle Ball performer and his new album Love Goes is out right now and it's absolutely incredible.
"And he is one of the sweetest and kindest and funniest people I've ever met. Please welcome the incredibly talented Sam Smith."
The festive special was pre-recorded by the stars at different locations.
Both the introductions and performances were pre-recorded for the Jingle Ball.
It comes after Sam opened up about the "really, really hard" backlash following their non-binary announcement.
They told James Corden on The Late Late Show: "All in all, it's been wonderful, I've always felt the way I felt.
"Being able to tell everyone that and feel so much more open about certain parts of my personality and my life has been absolutely incredible."
Sam went on: "It's been amazing, but it's also been really, really hard to see all the backlash and the amount of people that are still so unsupportive of gender nonconforming people and trans people all around the world."
