Alison Slavin, adopted as a child, realised Sam Davies was her half sister when she discovered the name of her biological father

They look and sound alike, have the same job, a similar taste in clothes and jewellery, and over the years have often been mistaken for siblings.

But it still came as a huge shock to Alison Slavin and Sam Davies when more than 15 years into their friendship they found out they really are sisters.

Slavin was adopted as a child but earlier this year found out who her biological parents were. She realised at once that her father had the same name as her best friend's dad – and a DNA test later confirmed that he was the same man, making them half sisters. "We had joked in the past we were sisters and people used to always ask us if we were, saying we looked alike," said Slavin, who was a bridesmaid at Davies's wedding before they knew of their blood tie. "But I was shocked to find out we were actually half sisters."

The women live a mile apart in Bristol. They met in 1993 through a mutual friend, used to go to karaoke twice a week, and soon became best friends, sharing the same taste in clothes and jewellery.

Slavin, 41, told how the colour drained from her face when she found out the name of her biological father because she saw immediately the possible link with her friend.

When the relationship was confirmed Slavin could not get through to Davies on the phone so she sent a text message saying: "Hello sis."

Davies, 43, said: "When Alison texted me telling me we were sisters a tiny part of me thought she was joking but a bigger part thought: 'Oh my God.'

"After the initial shock I spoke to Alison and she explained everything and I thought: 'Wow.' I had always wanted a sister, and what better sister could I have than my best friend?

"It's sad we didn't find out sooner but you can't change what's happened. We're just absolutely thrilled we have found out now."

The women, who are both childminders, have bought matching charms for a bracelet to show they are sisters. Davies said: "The charm is a silver book which has the words 'once upon a time' on it because we thought it was relevant because this is such a nice story."