Julia Roberts' ex-boyfriend Jason Patric is fighting for custody of the son he had hoped to keep a secret.

The Speed 2 star donated sperm so his ex-girlfriend Danielle Schreiber could have a baby three years ago (09), but now he wants to be a proper dad.

News of Patric's biological son, Gus, didn't make headlines until now because Schreiber agreed not to tell anyone who the father of her child was.

The couple briefly reconciled last year (11), and it appears the actor took a liking to his son - because now he has split from his ex again, he wants to be a part of the child's life and he filed legal documents in a family court earlier this year (12) asking a judge to award him joint custody.

Although by law he's little more than a sperm donor, and therefore has no custody rights, Patric has been awarded visitation, while his ex was granted temporary sole legal and physical custody of Gus.

According to Tmz.com the boy's mother has taken issue with the order because she doesn't believe her ex should have any legal rights to custody or visitation.

The case is ongoing.