This is 19-year-old Ethan McMullan and his sister, 17-year-old Alana – they live in Decatur, Mississippi. The two are best friends and love going bowling.
Ethan told BuzzFeed News that his sister has a brain tumour. "She has had the tumour for a very long time but we just found out about it on 6 March and had her surgery on 14 March. She's coping really well and staying positive about everything."
A day after his sister's surgery, Ethan got a haircut that resembles her surgery scar.
Alana was really blown away by what her brother did, so she shared it on Twitter where it gained over 98,000 likes.
"I got the haircut just to show her that she wasn't going through all of this alone," Ethan said. He added: "To show her that her scar was something to be proud of and show off. She loved it when she saw it!"
Ethan can't believe how viral his sister is. "I love that everyone has seen my haircut but I'm just glad that everyone is seeing it and praying for her," he said.
Lots of people felt emotional after they saw Ethan's kind gesture.
Victoria Sanusi is a reporter for BuzzFeed News and is based in London.
Contact Victoria Sanusi at firstname.lastname@example.org.
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