Sister of Las Vegas massacre victim recalls final moments, reveals boyfriend was about to propose

Athena Castilla — sister of Andrea Castilla, who was gunned down in cold blood in Sunday's violent Las Vegas shooting — told ABC's "Nightline" correspondent Juju Chang that her sister essentially died in her arms at the Route 91 Harvest country music festival after being shot in the head.

What happened?

The girls were celebrating her birthday at the festival with Andrea's boyfriend, who planned to propose later in the night.

"I told him she would have said 'yes' immediately," Athena said.

Athena then recalled the moments shots rang out and panic set in.

"My sister said, 'Duck,' so we duck, and the next thing we know she was already hit," Athena recalled. "It just happened so fast."

Athena said that Andrea was hit in the left side of her head. Grievously injured and bleeding profusely, Andrea dropped to the ground, Athena with her.

Athena revealed that despite all of the blood and the terror unfolding around them, she tried to shield her sister as much as possible, shots still piercing the air and people trampling over one another to get to safety.

"She was struggling to breathe and I just held her head," Athena said. "I’ve never seen so much blood in my entire life."

Athena said that she and others attending to Andrea eventually were able to transport her to a pickup truck, which was shuttling victims to nearby hospitals for care.

"We couldn’t give up on her," Athena wept. "She deserved a chance to get help ... she was literally dying in my arms.

"I was trying to stay positive that she was going to make it, but I could see all the blood, Athena added. "It was all over me."

Andrea died that night despite making it to the hospital.

A GoFundMe page has been set up for Andrea's family, and so far it has amassed nearly $65,000 in just two days.