Britney Spears Slams Jamie Lynn Again as 'Scum': 'I Wish You Would Take a Lie Detector Test'

The 'Toxic' singer went after her sister following a discussion of the 'Sweet Magnolias' star's memoir on 'The Real.'

The war of words between Britney Spears and Jamie Lynn Spears is seemingly not going away anytime soon, as the "Toxic" singer once again slammed her sister as "scum" over her memoir, Things I Should've Said.

Britney took to Instagram on Friday and posted a lengthy caption in which she goes after Jamie Lynn for a myriad of reasons, from the timing of her book and sarcastically congratulating as a "best seller" to accusing her of lying. Britney posted the caption alongside a video of an episode from The Real, where the panelists discuss the memoir.

"National best seller ???? DUH 🙄 …. the timing of your book was unbelievable Jamie Lynn … especially knowing the whole world had no clue what was really done to me !!!!" Britney penned to start the post. "My whole family including you is saying YOU DIDN’T KNOW …. Bull**it !!!"

One of the panelists, Adrienne Bailon Houghton, took Jamie Lynn to task while introducing the segment.

"She should have named this 'The Things I Should Have Said to My Sister and My Sister Alone But Instead I've Decided to Make a Book for Profit,'" said Houghton before the group discussed the ongoing feud between the Spears sisters.

"If you wanna clear your name ... who is it important to clear your name to: your sister or the masses of people?" Houghton added. "Why did you feel the need to clear your name to millions of people who are not your family members, who are not your blood, who are not your DNA?"

Britney addressed Bailon's comments in her post too.

"What these women are saying here is pretty clear !!!!" she wrote. "I'm just kinda shocked that more people like these real soul sisters aren't telling it like it is !!!"

The GRAMMY-winning singer went on to accuse Jamie Lynn of lying, so much so that the singer wrote, "I wish you would take a lie detector test so all these masses of people see you’re lying through your teeth about me !!!!" Britney also accused Jamie Lynn of "making money off of me" before signing off with, "You are scum, Jamie Lynn."

Britney's scathing comments come after and Sam Asghari's recent trip to Hawaii. A source told ET that the couple jetted off after Jamie Lynn appeared on Spotify's Call Her Daddy podcast and spoke about growing up with her famous sister, Britney's romances and an alleged incident with a knife that Britney denied.

"The second that Jamie Lynn’s interview with Call Her Daddy happened, Britney knew she wanted to get away," the source said. "Britney and Sam planned a trip to Hawaii to get a change of scenery shortly after. Britney felt overwhelmed and needed an escape."

Earlier this month, Jamie Lynn seemingly responded to Britney's first "scum" remark by posting a cryptic quote on Instagram. The quote read, "Nobody trashes your name more than someone who's afraid you'll tell the truth."

The social media post came following a fiery exchange between Jamie Lynn and Britney, who accused her younger sister of stooping to a new low "with these crazy lies for the Hollywood books!!!!" 

The feud has evolved to lawyers getting involved, after Britney's lawyer sent Jamie Lynn's lawyer a cease and desist letter in an effort to get the Sweet Magnolias star to stop mentioning her or sharing stories about her while promoting her new memoir.

For her part, Jamie Lynn has not responded to Britney's recent remarks. Jamie Lynn's last post on Instagram came Friday when she touted her book as national bestseller.