Daniel Radcliffe stopped by 'The Tonight Show Starring Jimmy Fallon' on Tuesday, but he probably wishes he’d packed some spare underwear. The Harry Potter star faced off with the talk show host in a game of ‘Water War’, which left him completely soaked, just minutes before he had to go to a premiere.

Daniel RadcliffeDaniel Radcliffe faced off with Jimmy Fallon for a game of 'Water War' on Tuesday.

The rules of ‘Water War’ are simple, each contestant takes a card from the deck and whoever draws the highest number gets to pour a pint of water over their opponent. The first to five wins. As the game began, things looked pretty good for Radcliffe as he took an early lead.

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But Fallon soon caught up at a one point he broke from the rules to pour a the glass of water over Radcliffe’s crotch. "You b******," the actor laughed. "You know what, for the record as well, just so everyone knows - I'm going to a premiere after this and I don't think I've brought more underwear.”

As the game ended, Radcliffe had to endure one more soaking as Fallon fired a water gun in his face. Sporting a newly shaven head, the Victor Frankenstein star took it all in his stride, telling Fallon, “thanks for having me”. 

Earlier in the show Radcliffe also made a surprise appearance at the end of Fallon’s monologue, to goad the host into performing the ‘Gangnam Style’ dance. As Fallon argued with audience members who tried to pursued him to do the dance, Radcliffe was shown giving the host a little extra encouragement.

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"Now, listen to me, James Fallon," Radcliffe said. "I didn't swim here all the way from England not watch you not do the 'Gangly Style' dance, OK? Hit the music." Fallon then did the infamous dance before telling Radcliffe: “There! Are you happy?” "Eh," Radcliffe replied. "It wasn't as good as I imagined it would be."

Watch Daniel Radcliffe and Jimmy Fallon play 'Water War' below: