BRITNEY Spears' sister Jamie Lynn claimed the "erratic" singer once "locked them in a room with a knife" as her "scary behavior spiraled.".

While talking to Juju Chang, Jamie Lynn was asked why she detailed the moment in her new memoir, Things I Should Have Said.

Also during the interview, Jamie Lynn alleged Britney, 40, previously grabbed a knife and locked them both in a room.

While reflecting on the alleged incident, Jamie Lynn said: "I was scared.

In recent months, Britney hasn't held back by slamming Jamie Lynn and their parents for how she was treated during her conservatorship.

When asked what "caused the rift"between her and Britney, Jamie Lynn replied through tears: "That love is still there.

The actress then opened up about her involvement in the conservatorship, sharing that Britney asked her if she "could be the person who assured that her boys got what they needed.”

After calling herself Britney's "biggest supporter," Jamie Lynn claimed she tried to give her the resources to get out of the conservatorship

Britney Spears' sister Jamie Lynn claims star 'locked them in a room with knife'