Luka's film was chosen out of nearly 2000 submissions from more than 40 countries and will be screened in New York City's Times Square.
"It's just the most amazing news I've ever gotten," says Luka.
"I was like screaming, jumping around it made my week. Since then every morning I've been waking up and counting down the days when I'm gonna go to New York because I'm just so excited."
Luka says it feels like he is taking Kosta to New York, like they always talked about.
"New York has always been Kosta's favourite city and he always wanted to go there. For me that's very special because as a big brother, it feels like I'm taking Kosta to New York.
"I can tell in my heart that it will make Kosta so happy."
Luka started making videos when his brother fell ill because it would "cheer him up and make him very happy".
Our Superheroes was a way to tell his story about Kosta and raise awareness about cancer.
"I wanted to do it to talk about my story about Kosta and just show my grief and how losing a child and a sibling to cancer is extremely hard and traumatic.
"I hope that my film inspires [people] to get up there and do whatever they can for a cause."
September is Childhood Cancer Awareness Month. For more information on how to help, visit the Child Cancer Foundation website https://www.childcancer.org.nz/ .