Well, that was awkward.

Coffee shop singer Kekoa Alama was blissfully unaware that a patron who got in on his performance was the star who wrote the song.

Together, the two sang reggae ballad “One Day” by Matisyahu, while Alama played the ukulele in the Hawaii hangout.

At the end of the impromptu duet, the two shook hands while Alama said, “You have a beautiful voice, man” — not knowing the incognito customer was Matisyahu himself.

“You know who wrote that song?” the artist asked, and then pointed to himself. “I’m Matisyahu.”

The reggae star was in town for a music festival according to local media.

Seemingly starstruck — and likely embarrassed — Alama attempted to play it cool mumbling, “I knew the sound of your voice man, I was like ‘no way!'”

Listen to Matisyahu’s version of the 2009 hit “One Day” below: