I've seen this frequently with kings, and occasionally with my corns. If you think about it, kings are more likely than not to encounter prey along watercourses in the wild (e.g., water snakes), and should be unperturbed by water or wet prey. It should have no ill effects as long as the water is clean to start with. If anything, it is probably good as he will get a little extra moisture.
If it bothers you, remove the water bowl before feeding. The day before would be best - definitely not if he already is in feeding mode! Otherwise, remember to refresh the water after he's done dunking his meal!
Good Luck,
John D
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1.1 Creamsicle Cornsakes
1.0 Bairds Ratsnake