College Student Attempts to Find Information About His Sperm Donor. He Made A Shocking Discovery That … Read more

So, one Sunday last May, feeling both bored and curious, Sanderson, a theater student at Indiana University, decided it was the perfect time to explore his paternal family history.

Despite being across the country from his home in Los Angeles for a theater role in Indiana, he called his mom, who eagerly joined him in the search. Together, they logged into the sperm bank’s website, which featured a sibling registry and chat room where siblings of the same donor could leave messages to potentially connect with one another.

When Sanderson, who had grown up only with his mom and pets, opened the chat, he stumbled upon a message from 11 years ago.

“It basically said, ‘Hi, my name is [name], and I’m your half-sister…'” Sanderson recalls to PEOPLE exclusively. He was surprised to discover that the message was from a girl who also had a full sister conceived using the same donor.