YouTube star and singer of the hit song "Clouds," Zachary Sobiech, died this week at the age of 18 after his brave battle with osteosarcoma. He leaves behind a legacy of positivity that will not soon be forgotten.

Sadly, his death was not unexpected. Sobiech had been battling the disease ever since he was 14. He did not become famous for his disease, however, but rather for the way in which he refused to let it put a damper on his spirits.

"Zach was at home and at peace with those he loved most. Zach's life ended just as he lived, embraced by the love of his family, friends, grace and music," the Children's Cancer Research Fund announced on its website.

Sobiech had first been diagnosed with osteosarcoma when he was 14. He had been running with his sister when he felt an unusual pain in his hip. After going to the doctor to get his hip examined, the news was worse than he could have possibly imagined.

Since his diagnosis, Sobiech has battled the disease with an attitude of unparalleled optimism and maturity. As a gift to his family and those who care about him, Sobiech recently made the song "Clouds" in reference to his impending death. Despite the inherent sadness of his situation, the song, now a hit on YouTube, brims with his positivity.

"Our family has been blessed not only by his amazing presence in our lives, but also by the love and support of our family and friends and by so many people in the community," the Sobiech family said in a statement. "In particular we'd like to thank those people who listened with their hearts and helped Zach bring his message and his music to the world."

Sobiech's song has now reached 4.7 million views on YouTube and has quickly gone viral on sites such as Facebook. The music video for "Clouds" can be viewed here. He has uploaded several more songs as well, some with childhood friend Sammy Brown.

"His music touched millions, and he leaves a lasting legacy that will help other young cancer patients through the Zach Sobiech Osteosarcoma Fund," John Hallberg, CEO of the Children's Cancer Research Fund, said in a statement. "Zach once said, 'You don't have to find out you're dying to start living.' He taught us all how to live, and we are all better for having known him."

A documentary by the YouTube channel SoulPancake has also gone viral after being published less than a month ago. It already has 6 million views. Check it out at the top to see the whole story of Zach's life and battle with osteosarcoma.