A 12-year-old boy died trying to save his younger brothers from a fire in their Milwaukee home — unaware that they had already escaped to safety.

The preteen, Adrian Cross, 12, became trapped on the second floor of the home during the late Monday night blaze, his grandmother, June Cross, told local station FOX 6.

“He went in to get his brothers,” Cross told the station. “That’s what he was trying to do.”

But Adrian had no idea that all of his 10 family members — six adults and four children — had made their way outside and were OK, Cross said.

“All of a sudden, [the family] started screaming,” she recalled.

She mourned the loss of her grandson on Facebook Tuesday, posting a photo of Adrian wearing a helmet.

“Last night we lost a Lil brave [boy], our grandson Lil Adrian,” she wrote. “He try to save his Lil brother’s in fire that took his life [and] it’s hurting the family right now…and we know the LORD has Him. We love you sweetheart.”

Prayers and condolences from friends and relatives poured in under the post.

“Praise God for his courage that was Christ-like,” one commenter wrote. “Laying down his life for others. Praying for comfort.”

“This is a hard pill to swallow,” wrote another. “My prayers are with the family. He was a hero on earth and now he’s a hero forever.”

The family is relying on their faith to cope with the sudden tragedy, Cross said.

“Through God, because that is the only strength we’ve got,” the grieving grandmother told the station. “I know God has better plans for all of us.”

The quick-moving fire started on the first floor, but soon engulfed the home — which had no smoke detectors, fire officials told the outlet.

“Our first companies were on the scene in three minutes,” said Milwaukee Fire Chief Mark Rohlfing. “Unfortunately, the fire was too far along.”

In a visit to the neighborhood the day after the blaze, Rofling urged families to install smoke detectors and “think about having a meeting place outside.”

The cause of the fire remains under investigation, and then Red Cross is assisting the family, according to the report. No one else was injured.