Chess Opening Theory/1. e4/1...e5/2. f4/2...Bc5/3. fxe5/3...Qh4/4. Ke2

King's Gambit Declined 4.Ke2??
This is a blunder on white's part. The only other legal move would be to play 4. g3, which would force Black's queen to retreat. This move leads to checkmate if Black plays 4...Qxe4#.

Next move probability
4...Qxe4# 100%

Win probability
Black 100%, White 0%, Draw 0%. (Note: the sample size for this is very small as players rarely make this blunder).