(CNN) A 12-year-old Texas boy saved the lives of his great-grandparents by wresting a knife away during a stabbing attack while driving Sunday.

The boy's half brother, Lucian Adrian Johnston, 20, allegedly stabbed his great-grandparents in the head and neck from the backseat after he was told he could no longer live with them as a result of his behavior, according to the Harris County Sheriff's Office.

Before the stabbing could turn fatal, 12-year-old Sacha was able to pull the pocket knife out of Johnston's hands and throw it out a window, the boy said.

"What I did was I grabbed him from behind. I pulled him backwards trying to get him away from grandma," Sacha told CNN affiliate KTRK

"But I did grab the knife. I held that to his neck also. He bent back my finger, which is still sore right now. He head-butted me, which I have a loose tooth from that, but I do not really care."

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