Daniel Levy, his on and off-screen father Eugene, Catherine O'Hara, and Annie Murphy reprised their roles as the Rose family to share a rendition of the classic song as a thank you to the teachers who helped the 2020 students graduate despite the Covid-19 pandemic.

The quartet was joined by a host of their co-stars, including Daniel's on-screen husband Patrick, played by actor Noah Reid, and Emily Hampshire's character Stevie Budd.

As the group kicked off their Zoom performance, they made it through to the last line of the song, when Mariah herself jumped on to deliver the last line.

"Moira, darling, I hope you didn't mind that I jumped in like that," Carey said, referencing Catherine's on-screen alter ego, actress Moira Rose. "You all sounded so good that I had to get in on it."

Clearly stunned at the appearance of his hero, Daniel, in character as David Rose, screamed: "I think I'm having a heart attack!"

Mariah then shared her own message to those watching the YouTube special.

"To the students who had to deal with this bleak moment, congratulations on this historic accomplishment," she smiled. "To all the students and teachers, you are so appreciated. And I just want to say, Class of 2020, you made it!"

The superstar concluded her appearance by singing a few lines of her tune Always Be My Baby - the song Patrick sings to David as they wed in the finale of the hit show - leading David to pass out and scream: "I love you!"