In sealed court documents filed yesterday in Los Angeles County Superior, and obtained by news Web site TMZ.com, Payne claims Smith confessed to her in phone calls and instant messages that Birkhead is the father of her baby girl.
And she alleges he was also the father of an unborn baby the actress miscarried.
Payne also alleges in her declaration that Smith was taking methadone and Xanax in May, during her pregnancy.
The actress' pal claims she actually administered pills and that she "personally observed" Smith taking "a rather high dose of Xanax."
Payne says she met Smith last summer in the Florida Keys, where they spent "several days" with their mutual friend, real estate developer G. Ben Thompson, who is now trying to evict the busty blonde from her home in the Bahamas, which he claims is his.
Payne also says Smith herself said her attorney Howard K. Stern wasn't the father of her baby girl Dannielynn. Stern insists he is the biological father.
But, in her declaration, Payne says, "I asked her why she did not just go into a relationship with Stern, to which (Anna Nicole) responded,
'Ewww...gross! No way! I would never!'"
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