What is the story behind Jason and Michael on General Hospital Soap?

Michael is Jason's brother A.J.'s biological son. Making him Michael uncle. When Michael was born his mother Carly didn't want A.J. to know that Michael was his son. So she asked Jason to claim Michael as his own, which he did.

After Michael was born Carly slipped into Postpartum depression and left Michael with Jason for a while. Jason accepted his role as a father to Michael and raised and protected him.

Although Michael was eventually adopted by Sonny, Jason has always remained a big part of his life.