The former model said he and his ex-boyfriend Alex, whom he dubbed "the doctor," were both sperm donors.
"A French lesbian had asked if we would be sperm donors," he told Banks. "So we thought, 'OK, you want me to do you?' And she was like, 'Ooooh, I'm not that talented.' So I said, 'Okay fine.' So we did a little test tube."
Although he said he isn't the biological father (his ex is), Miss J added that he is still actively involved in Boris' life.
In his new book "Follow the Model" (which hits shelves today), he writes: "The experience has enriched my life beyond imagination." He said his son is "an incredibly smart child. He was toilet-trained at a year and three months. He refuses to drink out of plastic and will use only glass."