Her husband cheated. So she wrote an open letter to his mistress.

A US woman has penned a scorching open letter to her husband’s mistress after discovering their affair. The sarcastic letter, which she posted to Craigslist, has since gone viral.

She wrote, “He’ll use you up, he’s a selfish lover, he’s a spend-a-holic, and it’s likely he’ll revert to booze. His financial decisions will drive you into bankruptcy. (He’s done it twice.) His family will hate you (they’re weird, you’ll see), and he has a tendency to do incredibly stupid stuff,” she wrote.

“You left your mascara in my husband’s old vehicle (he bought a newer one in late September),” she writes. “It was a shimmery brown Covergirl. I think you left some clothes here too. I threw them away. You also left a bra. You’re size 36 B. I’m a 34C. The bra stank with BO."

She also warned the mistress not to expect the high life with her 56-year-old husband, as half of the marital assets would be hers after the divorce.

“So you won’t be living in my nice house, we’ll be selling it. And he may not have mentioned all my grad school debt … We’ll be splitting that as well. So guess what you have???

“Be aware that everyday, he wrote me loving, wonderful messages, just as he was talking to you and wooing you. As far as I knew, we were strong in our relationship. If he’s been telling you something different, get my number from him, and let me show you the messages.

WATCH one man catch out his cheating partner. Post continues after video...

“He’s courting you as the next Mrs., knowing that our divorce will leave him very, very financially screwed,” she cautioned. “And you, my dear, are lookin’ to him like his life boat. Get out while you can. GOOD LUCK WITH HIM! THE PACKAGING IS DAMAGED AND WHAT’S INSIDE IS PRETTY SPENT, TOO!”

Ice cold. All the best to the wife - but judging by that ferocious letter, we're guessing she'll be just fine.

Have you ever dealt with infidelity in your relationship? How did you cope?