Dad secretly smoking behind mom's back

Gah I asked a question yesterday but it got deleted.
So yesterday, I caught my dad smoking in the kitchen even though he has claimed to have stopped for over a decade. I caught him buying some cigarettes a few weeks back as well.
I'm sure my mother...

does not know about this because she absolutely loathes smokers.

I don't know what to do. Am I supposed to tell my mother about this?
If yes, how should I go about doing it?

I don't want her to get hurt later on by finding out through some outsider about my dad's dirty habit.
At the same time, I'm so reluctant to tell my mom because I don't want to cause any family problems.
But it does seem inevitable that there will be family problems if she finds out from someone else.

I've tried asking my dad nicely to stop but he just denies he still smokes.

Help?

I had the same thing happen to me when I was younger except I found the cigarettes in my dads car. I decided that I had to tell my mom and I just simply sat her down and asked her how much she loved my dad. She said a lot, and then I told her that I didnt want to get my dad in trouble but I found out that he was smoking and I just thought she should know. She actually took it suprsiingly well, and she helped my dad quit.

Advise your father to talk to a rehabilitation counselor or the like. I dont think you should tell your mother...knowing mothers (assuming she's middle-aged and hitting menopause) emotions may flare

It isnt your place to tell your mother. I know you're trying to help, but you need to talk to him about this...