“Both of Britney’s boys are very well-behaved and well-mannered. What happened with Jamie and Sean was very unfortunate and definitely not right,” says the source, who adds that their alleged fight on Aug. 24 began after Sean “locked himself in a room” after his grandfather asked him to do something “he wasn’t interested in doing.”
Jamie, 67, “got very angry,” and according to The Blast, then broke down the door. “There was physical contact that made Sean scared and upset,” says the source. “Britney got upset as well and ended their visit with Jamie.”
The 37-year-old singer — who now shares about 10 percent of custody of her kids with ex-husband Kevin Federline — “can’t believe that her dad would jeopardize her relationship with her boys,” adds the source. “Britney is always terrified that she will lose custody.”
A rep and a lawyer for Spears did not immediately respond to a request for comment from PEOPLE. Jamie also did not respond to calls for comment.
The day after the alleged altercation, Federline, 41, filed a police report at the Ventura County Sherriff’s station with his lawyer Mark Vincent Kaplan. “Kevin got extremely angry when he heard what happened,” says the source. “His reaction does seem appropriate.”
According to Kaplan’s testimony as recorded in the police report, Spears’ 12-year-old son Jayden was also present during Jamie and Sean’s fight.
“Britney did the right thing and removed the children and took them out of there,” Kaplan previously told PEOPLE, adding that Federline still wants his sons to have “continuing and meaningful contact with their mother.”
Spears’ sons were also recently granted a restraining order against their grandfather that was filed by Federline and Kaplan.
Kaplan confirmed to PEOPLE earlier on Tuesday that Spears and Federline came to a new child custody arrangement last week which gives Spears 10 percent of custodial rights and Federline 90 percent. Kaplan tells PEOPLE Spears’ visits are required to be supervised.
While gearing up for a return to the Las Vegas strip with her show Domination after taking her wildly successful Vegas show Britney: Piece of Me on tour over the summer, Spears announced that she was taking an indefinite break from work in January to support her father.
In 2008, a Los Angeles court named Jamie permanent conservator of Spears’ affairs. He was also named permanent co-conservator of her estate, along with an attorney, Andrew Wallet.