Boy Who Asked for Birthday Cards Dies Due to Brain Tumor

— -- A 6-year-old boy whose request for birthday cards went viral has died after an 18-month battle with brain cancer.

Danny Nickerson died earlier this month due to complications from diffuse intrinsic pontine glioma. He had been diagnosed in October 2013 with the disease, which is one of the most chemotherapy-resistant cancers.

Danny's mother, Carley Nickerson, announced that the boy had died on the family's Facebook page last week.

"My precious sweet boy earned his angel wings earlier this afternoon after a courageous 18 month battle," Nickerson wrote. "Our lord came and carried his body to heaven. His body was so tired of fighting. He is now cancer free and running and playing and laughing with God and all of the other precious children."

Danny became famous last year after his birthday wish went viral. Already battling brain cancer for months, the boy's wish for this sixth birthday was to get cards from all over the world.

Danny's mom started to spread the word on social media and the request eventually went viral. The family received tens of thousands of cards in the months leading up to Danny's birthday. Even as the boy underwent treatment, a total of 33 radiation treatments and two clinical trials of chemotherapy, the family kept receiving cards.

On Danny's sixth birthday he was able to visit his local post office, where nearly 100,000 cards had been sent. The boy had so much mail he was able to climb on top of boxes with letters.

The family was also gifted with a special trip to Legoland and a meeting with New England Patriots Owner Bob Kraft.

ABC News' Yazhou Sun contributed to this report.