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Pop star Zac Hanson was left reeling in disgust when a stranger sneaked onto pop trio Hanson's tour bus on Monday in Seattle and spat in the drummer's face.

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The band was making its way from a soundcheck session at the Neumos venue in the city to their bus, which had been parked outside, when the passerby hopped onboard and assault the musician.

He was immediately kicked off the vehicle, and video footage of the run-in has since been posted online.

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Alongside one clip on Instagram, one fan, using the name triciajmartin, wrote in the caption, "This [expletive] snuck on Hanson's bus then spit on Zac's face.

She added, "He was just a random dude. Not a fan or anything. He was walking by the line, stopped to ask who we were seeing, and then started going off on us about how we didn't have a life because we were at a Hanson concert. Then Zac and Taylor came out of the venue and into the bus. He saw them, jumped on the bus behind one of Hanson's crew. He was on the bus for about 2 minutes, then the door opened up and Zac was shoving him out the door."

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Hanson refused to let the odd encounter ruin his mood and later took to his Twitter page to write, "Gonna be a good show tonight, I cleaned off all the spit and I am... ready to go!"