Two boys killed by falling tree as they camped in Yosemite: 'Our hearts are forever broken'

Two boys who were killed by a falling tree branch as they camped in Yosemite have been identified.

Dragon Kim, 14, and Justin Lee, 15, both from Orange County, California, were asleep when the oak tree branch fell on them as they stayed with family at a busy campsite on Friday.

In a letter to Dragon's water polo club team, his father paid tribute to his son.

Read: High School Football Player Dies, 5 of His Friends Injured in Midnight Boat Crash

"We are in deep sorrow and mourning," they wrote. "Dragon's mother, sister, and I are home but our hearts are forever broken."

They also thanked team members for their love, and for the joy they had brought the boy.

"Dragon, we love you so much," his letter continued. "Thank you for bringing so much love, laughter, and music to our lives. You are our precious son and you will live on with us."

The boys were killed around 3am on Friday.

Read: Batman Impersonator Who Visited Sick Children in Hospital Dies After Car Strikes His Batmobile

"I heard a loud crash, a loud boom," witness Daniel Moore told ABC7. "It almost sounded like a gunshot when it came down. I heard a woman screaming at the top of her lungs and I knew something was wrong."

The teens were already dead when rangers responded to 911 calls and reached them. It is still not clear what led the tree limb to fall on the boys and an investigation is underway.

A vigil will be held for the boys on Tuesday evening, according to ABC7.