YouTube star Daniel Coleman, better known online as Danny Go!, has announced the death of his 14-year-old son, Isaac.

The creator and host of the popular children’s YouTube channel shared the news Thursday on Instagram. The death of his eldest son — who was born with Fanconi anemia, a rare genetic condition that impairs the body’s ability to repair DNA — comes months after Coleman announced the teen’s Stage 3 mouth cancer diagnosis in December.

“Oh my sweet boy. There’s so much I want to say, but I don’t know how yet. I already miss you so much, and the pain in my heart is far more than I can process,” Coleman wrote, alongside a portrait of his son and a black-and-white image of him holding Isaac.

“But looking through thousands of pictures and videos this past week, I’m also filled with tremendous pride. Your 14 years were full of so many challenges, but you met them all with such grit…and you somehow kept your trademark joy in spite of it all. You truly had a spark like no other, Isaac!” he continued.

“Remembering how loved you were and how full of life your time here was gives me great comfort. Being your dad was the honor of a lifetime. I’m so proud of you and I love you forever. Rest peacefully, son.”

Coleman and his wife, Mindy, also have a younger son, Levi, who was born in 2015.

More to come