Yoon Hyun Sang and IU dropped a MV teaser for their upcoming duet, "When Would It Be."

The music sounds very dramatic, starting off with a slow piano before getting swept up by beautiful string instruments and escalating into Yoon Hyun Sang and IU's harmonized vocalizing.

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The dark lighting, IU's emotional facial expressions, and the poignant music all work together to send chills down your spine. �The full release will be on October 31.