Let's turn to the latest on Jason patric's bitter custody battle. He wants to be a father to the child conceived in vitro with his sperm. The mother says he's a donor with no parental rights. And the... See More
Let's turn to the latest on Jason patric's bitter custody battle. He wants to be a father to the child conceived in vitro with his sperm. The mother says he's a donor with no parental rights. And the two face off in court for a trial that could cause huge changes in our custody laws. ABC's Cecilia Vega has the story. Reporter: Jason patric calls today the most important day of his life. I have to win this for my son. I have to win this for fathers and mothers all over the country. Reporter: The '80s teen heartthrob who rose to fame in "The lost boys." Will be in a Los Angeles courtroom this morning, making an appeal in a bitter fight to be recognized as this little boy's dad. When was the last time you saw your son? 63 weeks ago. It's okay, I'll see you tomorrow. I've never seen him again. Reporter: Those words must be haunting for you. Yes because I lied to him. I say I would see him again. And I never showed up again. Reporter: Patric and Danielle Schreiber conceived Gus through in vitro fertilization. Their romance a custody dispute over their 4-year-old son. Schreiber said patric never signed a birth certificate. She says he was a sperm donor and therefore no present am rights. And a judge agreed, barring patric from seeing his son. Where is dadda? That's right. Reporter: But home videos like these prove he's been a dad from day one. Among his ammunition, forms he signed at the sperm clinic promising an intent to parent. Schreiber declined our request for an interview. Her lawyer said, we are spending our time preparing for the appellate argument. That's where we're going to use our ammunition. The question there is whether the mother also wanted him to be the father at the time the child was born. Reporter: An actor waging a war over what it means to be a dad. I will fight with everything I have to get my son back. Reporter: For "Good morning America," Cecilia Vega, ABC news, Los Angeles.
This transcript has been automatically generated and may not be 100% accurate.