1 / 9A MAN has revealed his horror after buying his girlfriend a DNA test for Christmas and accidentally exposing a family secret hidden for 30 years.2 / 9The well-meaning boyfriend bought the 23 and Me test as a fun gift for his other half, and even got her parents' approval before doing so, but it exposed something shocking in the family.3 / 9Posting in the 'today I f***ed up' section of Reddit, the anonymous American lad explained the test revealed his girlfriend has a secret half sister.4 / 9He wrote: 'She looks up the half-sister and she does not recognise her but recognises a few people in her circle. 'She looks up her father and gets his name. Confused she calls up her mom and puts her on speaker in our room.5 / 9''Mom do I have a half-sister?' Her mom replied 'Of course not, why would you have a half-sister honey lol'. 'Before her mum stopped chuckling she replied 'Do you know a John Smith?' The phone became dead silent.'6 / 9The confused daughter went onto tell her mum the test matched her with a half-sister, who has a dad called John Smith. The mum eventually asked 'have you said anything to your father?' then revealed a secret she's hidden for decades.7 / 9The boyfriend continued on Reddit: 'So apparently her mom and dad had 'taken a break' for a weekend and she hooked up with her x bf (john). 'Then got back with my gfs dad a couple days later. When she found out she was pregnant and they dated a possible time frame for conception.8 / 9'She knew it was probably not her husband's. She's kept this secret for 30 years. She told my gf to keep this secret.'My gf doesn't know what to do now and I'm just sitting here shaking my head at the audacity of her mom.'9 / 9People were horrified but also quick to reassure the boyfriend he had done nothing wrong. One wrote: 'For the record, the f*** up was entirely her mother’s for lying to her. You did nothing wrong and I hope you’re able to support her through this.'