Los Angeles: Former Playboy Playmate and oil heiress Anna Nicole Smith has been ordered to have her baby undergo a paternity test by January 23 as part of a lawsuit by an ex-boyfriend, his attorney said.

Larry Birkhead sued Smith in October, demanding she have the paternity test because he believed he was the father of a baby girl she gave birth to in the Bahamas on September 7.

Smith, 39, has said her personal lawyer, Howard K. Stern, was the father and they married in the Bahamas several weeks after the girl, Dannielyn Hope Marshall Stern, was born.

Superior Court Judge Robert Schnider ruled in Birkhead's favor in December and on Tuesday ordered Smith to have the paternity test done by January 23, Birkhead attorney Debra Opri said.

Smith's 20-year-old son, Daniel, died in the Bahamas three days after the birth of her daughter. A pathologist hired by the model said he apparently died from a drug overdose.