A woman discovered a text message from her boyfriend's mistress while he was sleeping, so she decided to get even.

On parenting forum Mumsnet, the woman explained she spotted a text message from another woman pop up on her boyfriend's phone while he was sleeping.

Instead of waking him up, she decided to get revenge.

"So my lying, cheating..... now (not that he knows it yet) EX is snoring away beside me. We have the same make and model of phone, and I'd plugged mine in earlier to charge, but didn't realize he'd taken mine out to charge his up while I was in the shower," she wrote via Mumsnet.

"A notification popped up, on what I thought was my phone plugged in, I went to read the message and saw it was from another woman, talking about how amazing their kiss was, completely baffled, I soon realized it was his phone," she continued.

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The woman revealed her boyfriend also spent several nights with the mistress while "he's been away at work."

"To say I'm heartbroken is an understatement, anger has overridden me but I want to play it cool before I dump his sorry, pathetic lying cheating f---ing a--!!!! I've set his screen saver to the last message she sent, so there's no way he can deny it," she concluded.

Users applauded the woman in the comments section, with many wondering how she was able to wait for him to wake up to inform him she knew about the affair.

"I don't know how you could wait. Nice touch though with the message on screensaver. What a ba---rd," one person wrote.

"I would throw the phone at his head to wake him up!!!" another commented.

"Ugh, I'm sorry. Is he staying at your place, or is this your shared home? If it's the first then I'd be waking him up with the big light on and his bag handed to him and all the rest of his crap so he can go home permanently. If it's your shared home tho he has as much right to be there as you have. You could string her along with a few leading questions pretending to be him, asking her what she enjoyed most and what she's most looking forward to next. And take photos of his screen for when he deletes them and tries to suggest you're 'crazy,'" someone else suggested.

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