He admits it was not planned and reveals that he only found out when an assistant called him out of a meeting saying his girlfriend needed to speak to him urgently.
He says: "This was not something I planned. But I remember going to the first scan with Lauren."
"I called him Tad because he looked like a tadpole. Something just kicked in. I felt unbelievably protective of both of them. I just absolutely wanted him. I just hadn't known that before."
In the exclusive, wide-ranging interview Cowell admits fatherhood has changed him out of all recognition, and provides touching insights into his new family life.
Though Lauren, 38, is now divorced, Cowell won't be drawn on any wedding plans, and the multi-millionaire says he is not a "conventional dad" to 21-month-old Eric, partly because he is "not a conventional man".
He doesn't change nappies or prepare feeds but is clearly devoted. He says: "I adore my son. We make each other laugh. We play with the dogs. I've taught him to share, to say please and thank you. Whatever he has he offers it to me."
Cowell also talks frankly about the future of his flagship show The X Factor, which has been hit by plummeting ratings and derision from critics. He insists ITV and its advertisers still love the programme but he is determined not to repeat the mistakes which have plagued the current series - such as allowing screaming audiences to drown out the acts and the judges.
He says: "I was on the stage with my contestants, I couldn't hear a bloody word of what was going on. That was one lesson learned, it will never be that bad again."
Cowell says such setbacks have been put into perspective by the death of his mother Julie following a stroke.
The former dancer, who died in July aged 89, was a driving force in his career and someone he could always turn to for advice. He refused to contemplate the thought of life without her even when doctors said she had just months to live.
He says: "I wouldn't listen. I kept saying right to the end that there was hope. And I wasn't prepared for it. You know it all happened in my 50s. I have a son and then I lose my mother. It changes you. I'm still going through it."
Cowell has an estimated fortune of more than £355 million, but says he is more inclined to give it to good causes than leave it to his son.
"I don't like the idea you just sort of pass it down from generation to generation. I mean, I find that quite disgusting. No one ever gave me a penny and I believe part of my drive was to do with the fact I had nothing to lose. That gives you a lot of energy."
- Mail On Sunday
