A man who discovered his girlfriend had been cheating on him decided to get his own back by writing her a 'surprise' card - and sharing it with the entire internet.

The man, known only as BinanoSplat and believed to be from North-West America, explained: 'Found out my girlfriend is cheating on me. Giving her this card tonight at my birthday dinner.'

In a post that has been viewed more than 1 million times, the 28-year-old man shared a series of photo on Imgur and Reddit showing the card he intended to give her.

Scroll down for video

After Reddit user BinanaSplat apparently discovered his girlfriend cheating, he decided to surprise her over dinner with a card addressed to 'Schmoopsie Poo' with an angry message and her house keys inside

The envelope was addressed to 'Schmoopsie Poo', and the message inside said: 'This card will feel heavy, because it's packed with good thoughts.'

However, the lovelorn man - who apparently discovered his girlfriend's infidelity after she left her Facebook Messenger open on her laptop - had crossed out the soppy message and replaced it with: 'Because it's packed with your house key.

He added: 'Now that you're single, you don't need to feel guilty about your sexually charged texts w/ Michael, going on dates w/ Jared, or about getting drinks tomorrow with Derek.'

Inside, he had sellotaped a house key to the card. However, before he got the chance to confront his girlfriend, his plan backfired when a friend stumbled across the post and showed her.

He gave her a card that read: 'This card will feel heavy (...) Because it's packed with your house key.' He later detailed all of her apparent infidetlities in a post which has now been viewed more than 1 million times

BinanaSplat posted an update entitled: 'IT'S RUINED... THANKS REDDIT,' explaining: 'Her bestie found this and called her. I don't know how he knew we were even still dating considering how she's been hiding that fact from everyone.'

He then relayed their entire conversation in which his girlfriend said that she had seen the picture and asked: 'Is there anything you want to say to me?'

After telling her that he never wanted to speak to her again, she apparently replied: 'I think you're disrespecting me,' causing her boyfriend to 'internally facepalm'.

He ended the conversation by saying: 'Go f*** yourself. I'll leave the key in your mailbox.'

After people bombarded him with more than 18,000 comments pressing for more details, he elaborated, saying: 'We were Facebook official. She kept the status hidden though so that she could date around while still "having a boyfriend".'

He added: 'I guess it made her feel good to have the title, but she sure as s*** didn't care about me.'

Thousands of people rushed to offer their condolences. Blitzgreg wrote: 'Happy birthday and I hope you're doing better now, or at least, on the way.'

Another said: 'Sorry to hear that her best friend ruined it bro. Hopefully you have a kickass birthday though. Don't let her get you down. Happy Birthday.'