'Lost Boys' Actor Jason Patric Takes Custody Battle to LA Court

May 8, 2014— -- Jason Patric calls today the most important day of his life.

The 1980s teen heartthrob -- who rose to fame in the movie "The Lost Boys" -- went to a Los Angeles courtroom this morning to make an appeal in a fight to be recognized as the father of a 4-year-old boy, Gus.

Patric and his ex-girlfriend, Danielle Schreiber, conceived Gus through in-vitro fertilization. Their on-again, off-again relationship has now become a high-profile custody dispute.

Schreiber said Patric never signed a birth certificate, that he was a sperm donor -- and therefore had no parental rights. In a statement to ABC News, Schreiber said Patric offered to donate sperm after the two broke up “under the express condition” that it be kept secret and “that he would not be a father to or have any obligations, rights or responsibilities for my child.”

A judge agreed, barring Patric from seeing Gus.

But Patric said he's been a dad from day one. His ammunition includes forms he signed at the sperm clinic promising "an intent to parent." He is seeking full custody.

Patric continues thinking about the last time he saw Gus.

"Sixty-three weeks ago," he said.

"I said, 'It's OK. I'll see you tomorrow.' I've never seen him again."

Schreiber declined an interview request, but according to her lawyer, "We are spending our time preparing for the appellate argument. That is where we are going to use our ammunition."