A woman who thought she was an only child was shocked to find out she had 77 secret siblings.

Sheena Holland-Dolan, from Cleveland in Ohio, US, grew up believing she was an only child. It was only when she turned 20 that she found out her mum and dad had used a sperm donor after struggling to conceive on their own.

“To say it was a shock was an understatement,” she told MailOnline. “I was left shaken.”

Now 26, Sheena has discovered dozens of other relatives out there and has even made lifelong friends with some of her half-siblings. But it wasn’t an easy journey to get to this point.

Sheena’s parents were initially told not to tell her the truth about her heritage, but they ended up spilling the beans about six years ago. She described initially feeling upset her mum and dad had lied to her but soon felt compelled to find out about her family history.

She turned to the website 23andme.com where someone quickly got in touch saying they knew who her dad was. Through the site, she found out she was the 47th sibling born to the same man.

She added: “The prospect of siblings hadn’t even crossed my mind when I went hunting on family tree sites.”

Sheena’s older half-sibling, Kianni Arroyo, had set up a Facebook group in a bid to connect as many siblings as possible. It was through this Sheena found out her biological father had become a sperm donor in college to earn extra money.

Now Sheena has embraced her unusual family background and loves finding new siblings to add to the vast network. She’s discovered new relatives as young as five.

So far, 78 confirmed half-siblings have been found at the time of writing.

Sheena with one of her half-siblings

She said her siblings all have “different levels of involvement” with the group – some, like her, regularly meet up while others prefer to remain more distant. Every time she meets a new sibling she will scour them for similarities, she added.

Kianni and Sheena even ended up growing so close they even went on honeymoon together. But the bizarre situation also has its downsides.

“It does worry me slightly that if I go on to have children, I will have to warn them that they need to be very careful when choosing their partners,” she confessed. “They will have so many close relatives out there who they will know nothing about.”

But she added: “I’d love to meet all of my half-siblings, eventually.”