The Irish singer, who enjoyed massive chart success with a cover of the late music mogul's Nothing Compares 2 U, stunned fans over the weekend (01May16) when she alleged Prince was a "longtime hard drug user" and suggested Arsenio was his supplier.
Sinead took to Facebook and wrote: "Two words for the DEA (Drug Enforcement Administration) investigating where (sic) prince got his drugs over the decades... Arsenio Hall (AKA Prince's and Eddie Murphy's b**ch)."
Sources told TMZ the Irish star also reported Arsenio to officials at the Carver County Sheriff's department, who are investigating Prince's death.
In his defamation lawsuit, filed on Thursday (05May16) and obtained by TMZ, Arsenio denies supplying Prince with illegal substances and also dismisses her claims that he once gave her drugs.
Arsenio goes on to insist that Sinead and Prince were never close, adding she only met the Purple Rain singer a couple of times and made it clear she "detested" him.
The comedian states O'Connor is "well known for her media antics and for seeking attention through inflammatory Facebook posts".
A representative for Arsenio previously shot down the allegations made by Sinead on Monday (02May16), insisting her claims were "absolutely false, ridiculous and absurd".
And later that day, Hall spoke to Access Hollywood and revealed he was still struggling with the image of his friend dying alone in an elevator at his Paisley Par home near Minneapolis, Minnesota.
"What pained me most is the visual image of where he passed, alone in that elevator," he told the U.S. news show. "That bugged me, so I've tried to just remember the positive... I'm really gonna miss him and I'm playing his music every day."