Not an easy task to let someone know he is not wanted anymore. 
Nevertheless it is a normal event in life's experiences for many women. Letting 'him know his situation' is for many the hardest task; as such a somewhat harsh, yet funny letter will make this a little easier.

It's ideal when sent with an accompanying short note. 'He' can even frame it for prosperity.

Dear John Letter
You are gone - you are done and dusted, busted, quite passie' you 
don't exist for me. You see, 
although you thought yourself adored, you bored me to distraction, stupefaction 
and I've gone and found another, brother, what a fool you are.
And here's the thing, I won't return your bling, 
I sing another song now that you don't exist for me.
I wish you all the best, I jest, I couldn't give a damn, poor lamb, 
that I led you to the slaughter. Yes, it's laughter that is ringing in your ears. But cheers, 
I've gotten rid of you at last, no need to weep into your beer. 
I hope I never hear from you again.
So, take the knife out from your heart and make another start, but make it far far far away. 
Go quickly, go fast, depart. And in another life, make another bitch your wife, 
a witch who will make your life a living hell. Do I hear a wedding bell?
Hey swell • it couldn't happen to a nicer guy - I lie.
Yours, never in this life pal.