Ethical Dilemma

Here is a golf ethics question:                                

You're playing the club championship finals and the match is halved after 17 holes. 
You have the honour and hit your ball 250 yards down the middle of the fairway, leaving a simple iron to the pin.
Your opponent then hits his ball, slicing it deep into the woods to the right of the fairway. Being the golfing gentleman that you are, you help your opponent look for his ball. 
Just before the permitted five minute search period ends [and you're further away from the pin], your opponent says:   "Go ahead and hit your second shot and if I don't find it in time, I'll concede the match."
You hit your ball, landing it on the green, stopping 20 feet from the pin. 
Just after your ball comes to rest, you hear your opponent exclaim from deep in the woods: "FOUND IT!". 
The second sound you hear is a ding, the sound of a club striking a ball and the ball comes sailing out of the woods and lands on the green, stopping six inches from the hole.
Now here's the ethical dilemma....

Do you pull the cheating scumbag's ball out of your pocket and confront him with it 
or do you keep your mouth shut?