Billie Eilish is back on TikTok, and she made one vocal coach's day after surprising him with a duet.

Sheridan Coldstream is a professional vocal coach, who has posts of him playing popular songs on the piano and encouraging TikTokers to sing along. So, when he picked Billie's "Listen Before I Go," he probably never expected the Grammy winner, herself, would respond.

Billie shoots the video from the ground up and grins toward the camera before launching into a gorgeous rendition of her 2019 track. She didn't caption the post but did link back to Coldstream's.

"This is the greatest possible compliment I could ever receive!! I couldn’t be more touched and flattered," the British vocal coach gushed in the comment section. "Still on a crazy high that this has happened! Just WOW."

The surprise duet has since turned into a joke, with fans pretending that the post was from someone who just so happened to look and sound exactly like Billie. Comments range from "This is a really great cover. I'm sure Billie Eilish would be proud" to "have you ever thought about going on Americas Got Talent?"

Prior to this, Billie hadn't posted on TikTok since March. Nearly 15 million people have watched her latest video.

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