The 45-year-old singer has logged on to his Twitter account to tell his 2.85 million followers that his sister-in-law Sara MacDonald was responsible for his older sibling Noel, 50, quitting the 'Supersonic' band in 2009 and the rift between the brothers which continues to this day.
Liam wrote: ''Think it's time to address the witch you want me to drop dead you have a screw loose and know the world knows as you were LG x
''She's the reason OASIS is no longer have to put it out there she's DARK [sic]''
Liam made his accusation in response to a post Sara is said to have made on an Instagram fan group after Liam joked in an interview that he ''didn't care'' if Sara, Noel or his brother's ''f***ing'' kid'' - 18-year-old model Anais, whose mother is the guitarist's ex-wife Meg Matthews - were harassed by social media trolls.
Sara - who has sons Sonny, seven, and 10-year-old Donovan with the 'Wonderwall' hitmaker - is reported to have posted: 'His f***ing kid''? You mean your gorgeous niece, you deplorable w***ker. Please god [you] have dropped dead by the time my kids are on social media. [sic]''
Liam has also alleged that Sara tried to sabotage an American tour by Oasis by hiding Noel's passport so he wouldn't be able to jet out to the US and perform his hits, resulting in him seeking solace at his younger brother's home.
The 'Wall of Glass' rocker tweeted: ''We were about to go on tour to USA she robbed noels passport f***ed with his head for a Wk he come crying at my door she's proper dark ... Yeah now we're f***ing talking you want more ... Cos if so I'm here all Wk [sic]''
Liam signed off his social media rant by comparing Noel and Sara to infamous British serial killer married couple Fred and Rosemary West - who were responsible for the torture and murder of at least nine young women between 1973 and 1987.
Referencing the insult Noel aimed at Damon Albarn and Alex James at the height of Oasis' Britpop feud with the pair's group Blur, in which he stated ''I hate that Alex and Damon. I hope they catch AIDS and die'', Liam tweeted: ''Him and her are like Fred and Mary west wishing people get aids and drop dead as you fucking were Oasis for life LG x [sic]''
After making his outrageous comment, some of his followers enquired as to whether the solo rock star had gone too far and had ''lost it'' but the 'Bold' songwriter insisted it was just time for the ''truth''.
Liam replied: ''Nah I've never lost it ... You should be scared the truth hurts don't it [sic]''
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