At 17, Bryan realised his sister wasn't who he thought she was. His response is going viral.

Last week Bryan Lara discovered a family secret.

The 17-year-old from Houston, Texas, found out his sister Pamela was actually his half-sibling, and that he was part of a blended family.

Pamela, an 18-year-old dancer, had discovered that her siblings were in fact her half-siblings when she was just 11 years old. She was sworn to secrecy.

Immediately after uncovering this family secret, Bryan wrote a letter to his older sister.

My little brother found out I’m not his fully sister and I came home to this.. I’m crying.. pic.twitter.com/DAC0yUUBt4

— Pam???? (@PamTina_) July 24, 2018

“I just wanted to let you know how much I love you. I don’t care what people say, you are always going to be my sister — my full blooded sister. You are the best thing that happened to me, I love you with all my heart,” the letter began.

“Thank you for helping me on my worst and thank you for leading me the right way,” adds Bryan, who is also a dancer. “I will always be there for you, just like you always been there for me. I love you.”

The letter was signed, “With love, your annoying brother”.

Accompanying the letter were a bunch of Pamela’s favourite snacks.

Pamela shared the letter on Twitter, it’s since gone viral.

“My little brother found out I’m not his [sic] fully sister and I came home to this… I’m crying,” she wrote.

Speaking to PEOPLE, Pamela explained why she kept the secret all these years.

“I had to keep it a secret from everyone just so it wouldn’t affect our family,” she explained. “And mostly because I was scared that I was going to be looked at differently by my siblings.”

“My older sister found out in the most unpleasant way, but it was a relief that she understood and agreed to keep it a secret,” she adds. “My brother ended up finding out sooner than expected from my sister through an argument.”

The letter has brought comfort to half-siblings around the world, with many sharing their own stories:

When my little sister found out our dad isn’t my biological dad she was so upset for me lol she cried and held me like she was gonna shield me from it ❤️

— LariLari ✨ (@honeysugarbeet) July 25, 2018

When I found out my oldest brother wasn’t my full brother I said and I quote “I thought he was different. But I like him more anyway”

— Aaliyah ???????? (@Its_Montana_) July 25, 2018

When my sister realized we didn’t have the same dad she told me I could share hers and she was gonna tell him to adopt me????

— jabon de quavo (@damarisssmd) July 25, 2018

Half or full it doesn’t matter. You still share blood. My half brother is no different to me then my full. We all share blood. Would you say a cousin isn’t family because they don’t have 100% of the same blood?

— Kristina (@teeniebeenie6) July 30, 2018

This is how I felt when I found out my sister had a different dad

— ???????????????? (@LeoneDaGod__) July 26, 2018