Britney Spears has referred to her sister Jamie Lynn Spears as a "selfish little brat" and said she was "f***ing hateful" when she was younger in a rant on social media.
The criticism from the pop singer, 40, comes whilst her younger sister, 30, is promoting a new tell-all book, Things I Should Have Said - which was released earlier this week.
The memoir by Jamie Lynn - known for Nickelodeon shows All That and Zoey 101 - is understood to discuss life within their family, which she's further talked about in interviews.
It hasn't gone without controversy though, with Britney appearing to have taken issue with her sister over the book - even ranting about her sibling on social media recently.
This included the musician - whose conservatorship recently ended - saying that she should have "slapped" Jamie Lynn in the past.
The outburst, which is said to have been posted on Instagram yesterday, seemed to have focused on Jamie Lynn getting an easier childhood when she was younger.
It's been reported that Britney has since reuploaded the post and shared further details about how she feels, according to an article by the Sun this evening.
Among the comments made in the post is a criticism that centres around the pop star having bought their mother Lynne Spears, now 66, a house earlier in her career.
Britney accused Jamie Lynn of being a "selfish little brat" for allegedly saying that it was "weird" for the Baby One More Time singer to make such a gesture.
She said: "You selfish little brat. Saying how weird and dumb it was that I bought a house for mamma! She was so proud and you told that interview girl that it was just weird."
Some of the post seemed to reference the early 2000s when Britney spent time at home with her family - with her referring to Jamie Lynn as a 12-year-old towards the start.
The Grammy Award winner later said her sister had been "f***ing hateful" towards their mother, claiming that she had been "shocked" at how Jamie Lynn "talked back" to Lynne.
And she also suggested in the recent post that Jamie Lynn hadn't supported her following the singer's high-profile break-up with Justin Timberlake, now 40, back in 2002.
She alleged in the social media post: "When I came home, you and your little friends all thought I wasn't cool. You felt bad for me in the break-up ... HELL NO ... you didn't."
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"You and your friends all dyed your hair like Christina Aguilera and you no longer would play with me anymore," she said.
The pop star later added in the post: "You shut me out when I needed you the most. Writing in your book saying I wasn't like your mom anymore ... No, you hurt me."
The Mirror approached a rep of Jamie Lynn for comment.
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