Britney Spears' father was allegedly so enraged during an argument with his 13-year-old grandson that he broke down a door to get to the young boy, and the incident has sparked a child abuse investigation.
We're told the boy became scared of his grandfather's reaction, so he ran into his room and locked the door.
Our source says Jamie broke down the bedroom door, and once he got his hands on the boy, allegedly "violently shook" the teenager.
We're told the entire incident was chaotic, but in the end Britney did the right thing by removing her children from the home -- and her father -- and bringing them someplace safe.
K-Fed learned about the incident after Britney called him to take the children for the night, even though it was technically still her time with custody.
The following day, we're told Kevin and his attorney, Mark Vincent Kaplan, walked into a Ventura County Sheriff's Office and reported the alleged crime.
Since the police report was taken, we're told all parties have spoken to investigators, and the case has been submitted to the Ventura County District Attorney for charging consideration.
We're told Jamie is more than likely facing a misdemeanor battery charge for allegedly "inflicting unjustifiable physical pain on a child."
Calls to Jamie Spears have not yet been returned.
As we reported, Federline went to court earlier this year to get more child support after he took over the majority of custody with the former couple's two children.
After lots of fighting between the two sides, they were able to hash out an agreement that gave the former DJ thousands more per month.