ST. LOUIS COUNTY, Mo. — A wrongful-death lawsuit filed Thursday against ex-beer baron August Busch IV over the accidental drug overdose death of a woman at his mansion set off a fight within her family over who has the right to pursue damages for her young son.

The case, filed in St. Louis County Circuit Court, claims Busch was negligent in the death of his girlfriend, Adrienne Martin, 27, and seeks unspecified damages for her son, Blake Alexander Martin, age 8.

The child’s father, Dr. Kevin Martin, is a plaintiff on his son’s behalf.

Christine Trampler, Adrienne Martin’s mother, told the St. Louis Post-Dispatch later in the day that she plans to intervene because she fears the friendship between Busch and Kevin Martin could color the outcome for her grandson.

“”I am going to be applying for custody of Blake and ask that a guardian ad litem (independent legal guardian) immediately be appointed for Blake for purposes of this wrongful death suit,”” said Trampler, who lives in Springfield, Mo.

She said she is working with New York lawyer John Q. Kelly, who has developed a high profile representing the mother of Natalee Holloway, the girl missing in Aruba, and the estate of Nicole Brown Simpson in a civil suit against O.J. Simpson. Kelly could not be reached for comment.

Kevin Martin has said since his ex-wife’s death that he and Busch were “”almost like brothers.”” On Thursday, Martin said he could not comment, on advice of his counsel, John P. Heisserer, of Cape Girardeau.

Busch’s lawyer, Maurice Graham, of St. Louis, filed an immediate court response to the suit, denying his client was negligent. Graham declined comment later. Busch could not be reached.

Both sides immediately obtained a judge’s order to move the case to Cape Girardeau County Circuit Court. Kevin Martin lives in Cape Girardeau with his son and practices osteopathic medicine there.

A legal expert said Thursday that Trampler faces a long, tough road in challenging Kevin Martin’s status.

“”The father has custody of the son and the court normally defers to the parent,”” said Peter Joy, a law professor at Washington University in St. Louis. “”Anyone challenging him will have to demonstrate he’s currently doing something tangible to harm his son. It has to be more than just saying it.””

The dispute largely centers around who has a right to pursue litigation.

“”The sole or primary beneficiary would be the minor child,”” Joy explained.

Joy said Adrienne Martin’s parents could still sue on their own, but that it would most likely be rolled into the current suit. He also said the monetary value “”for the death of an adult child isn’t very great.””

Joy said Martin would not be allowed to give Busch an unfairly low settlement even if he wanted. “”The court has an obligation to make sure any settlement is appropriate and in the best interest of the child,”” Joy said.

Authorities said Adrienne Martin’s death Dec. 19 in Busch’s mansion in Huntleigh was an accident, and that a hole in Martin’s nasal septum indicated “”several months to a year of cocaine use.””

Au autopsy put her cause of death as an overdose of the painkiller oxycodone; officials said she also had a lethal level of cocaine in her blood.

St. Louis County Prosecuting Attorney Robert P. McCulloch has said the death was clearly accidental and there was no information on which to base any prosecution. He said that neither Martin nor Busch had a prescription for the oxycodone, and that Busch stopped cooperating with the investigation after his initial police interview.

Busch, 46, was the chief executive of Anheuser-Busch before it was sold to InBev in 2008. The sale earned Busch about $100 million, and he started collecting about $120,000 a month as a consultant.

Busch told the Post-Dispatch in January that he had been battling depression and “”other issues”” stemming from the sale.

“”I would have given up my life to save the company,”” Busch said then, “”but I couldn’t do anything.””

Busch has been in controversy over a death before, when he was a college student.

Michele Frederick, 22, was killed in 1983 in the crash of Busch’s car in Tucson, Ariz. Busch was found hours later with a skull fracture, disoriented. No charges were filed. Cocaine was found in Frederick’s system.