"People blame him a lot, but Anna had her own mind too," Birkhead, the father of Smith's baby daughter, tells OK! magazine. "She had a choice and we were arguing and that's what happens. I'm thankful that everyone can get along for Dannielynn. How could you not?"
Is Dannielynn healthy?
"The doctors say she's fine and has met all of her developmental milestones," Birkhead says. "She's a really curious, alert baby."
Birkhead, 34, a Los Angeles photographer and ex-boyfriend of the late Playboy Playmate, had feuded with Stern, her longtime lawyer-companion, over the paternity of now 7-month-old Dannielynn.
A court in the Bahamas ruled last week that DNA tests proved Birkhead is the father. Stern said he would not fight to retain custody of the baby.
Father and daughter are featured on the cover and inside the magazine's latest issue, on newsstands Friday. A representative for OK! -- which pays for its exclusive interviews -- wouldn't disclose the terms of its deal with Birkhead to The Associated Press.
The magazine also has photos of Birkhead and Dannielynn.
Stern has been helpful, Birkhead says. "It seems unlikely, but he's been a great help. He's been with Dannielynn the last several months. He knows her likes and dislikes and things that could help me. He gives me credit when I'm doing good things and gives me tips on things I should do a little different."
Birkhead says Stern, who was listed on the birth certificate as Dannielynn's father, invited him to meet the baby about a month ago.
Dannielynn has been living in an oceanfront home in the Bahamas with Stern.
Birkhead isn't as generous with his comments on Smith's mother, Virgie Arthur, who is seeking visitation rights.
"It's puzzling for her to display affection to me and then for the attorneys to say she's going for custody and Larry was just a sperm donor and a one-night stand," he says. "Then they all come and shake my hand. You've gotta scratch your head and say, 'What's going on here?"'
"I'm willing to listen to see what people want, but that doesn't mean I'm going to agree," he says. "I hope I don't have to fight for the baby."
A lawyer for Smith's mother said Tuesday that talks with Birkhead have so far failed to produce a custody agreement concerning Smith's infant daughter.
Attorney Debra Rose said Arthur is still trying to reach a deal with Birkhead ahead of a hearing Friday on her petition for custody of Dannielynn, who could inherit a fortune from her mother's estate.
"We're still in negotiations. We're still talking," Rose said.
Arthur says she'd like access to her granddaughter and believes an agreement with Birkhead is possible.
"She truly cares. She deeply cares," Rose said. "Her faith in God leads her to believe that at the end of the day she will be in a position to assist with raising her granddaughter."
Smith gave birth to Dannielynn in September in a Bahamas hospital, days before her 20-year-old son, Daniel, died from a lethal combination of drugs at her bedside. Smith died in Florida in February at 39, also from a lethal combination of drugs.
Legal wrangling continues over the estate of Smith's late husband, Texas oil tycoon J. Howard Marshall II, who died in 1995. It remains unclear how much, if any, of the $500 million Marshall estate Dannielynn might inherit and whether her guardian would have access to the money.