Because Catholic priests take a vow of celibacy, those who father children are forced to keep it under wraps.
A New York Times report revealed last week that the Catholic Church has a set of secret guidelines for priests who have children, detailing what to do when the rule is broken.
After decades of detective work, a grave exhumation and a DNA test, Jim Graham found out that he was among those secret children.
His father is the late Thomas Sullivan, a Catholic priest from Lowell.
On getting confirmation from DNA testing that Father Sullivan was his father
"I knew from the day I saw the obituary photograph of my father's face and I had his eyes, I had his nose, I had his chin. So I knew what the results would be but still, it was very emotional.
On his mother's relationship with Father Sullivan
"It was a long relationship, it started back in 1945. My mother left Buffalo with me as a toddler. My father left the Order at the same time and we escaped from Buffalo and the church was insistent that he would come back to the Order and he wouldn't be out here as a loose cannon with a parishioner's wife and a baby. So private detectives were hired and they found us after about eight months and they took him back into the Oblate Order, put him in a camp up in Essex, New York for rehabilitation and they took me from my mother's custody and put me in the home of John Graham, her former husband to make it look like I was his son."
"All along, they knew who I was. And I knew that they knew that. But yet, they put me through this very difficult situation to exhume my father's body to prove it."Jim Graham, son of a Lowell Catholic priest
On how he thinks the Catholic Church should handle priests with children
"First of all, it should be transparency. You look in my case, and I still don't have transparency from the church because even after I got the results, I never heard from them. All along, they knew who I was. And I knew that they knew that. But yet they put me through this very difficult situation to exhume my father's body to prove it. And they knew all along. So, you look at the other children of priests and we all have unique situations, we're all different. But still, I think the Catholic Church is good at cover-ups, they're good at stonewalling. And the last thing they want to do is admit a fault that they made years ago."
To listen to the full interview, click the audio player above.
This segment aired on February 21, 2019.