LaToya Jackson is being sued by reality star Omarosa Manigault over allegations about the death of the latter's fiancé, Michael Clarke Duncan.
Michael Jackson's sister raised eyebrows after she claimed on TV that her rival killed the Green Mile star. He died of a heart attack in 2012.
After she was fired by Donald Trump from NBC's Celebrity Apprentice, Jackson lashed out at her TV rival during her exit interview.
In scenes which aired in the US the former singer said: "[Manigault's] a conniving, scheming, cut-throat," before alleging that Manigault was responsible for Duncan's death - even though she had been praised for her swift actions in keeping him alive for some time after he suffered the heart attack.
Manigault's attorney rushed to release a statement confirming that she planned to take legal action over the "false, vicious and defamatory" comments.
"Rev Manigault has been heralded as a life saver for her actions on the evening that her fiance suffered a life-ending heart attack. It is because of her bravery that Mr Duncan - the love of Rev Manigault's life - was able to live for months beyond that tragic night. Mr Duncan passed away from natural causes.
"Ms Jackson made the statement immediately after having been fired from the show and blames Rev Manigault for her loss. It is repulsive and of the lowest level for Ms Jackson, who showed herself to be a sore loser in making these disgusting statements in the wake of Rev Manigault's tragic loss.
"As her counsel, we have been directed to pursue these defamatory statements to the fullest extent of the law with LaToya Jackson and any other participating publications or media outlets who repeat or repost these statements."
It had been previously been claimed that Manigault, a former political consultant, kept Duncan alive by performing CPR after he went into cardiac arrest. He died in hospital in September.