Bowers unauthorised book, published last week, was the result of hundreds of hours of conversations with the media mogul.
He told ITV1s This Morning that he had spoken to Cowell since the contents became public.
It was a very, very interesting journey. There is a man whos actually very private in his life although he doesnt seem it. He keeps his secrets pretty well, he said.
I flew with him a lot to America on his private jet, I was on his yacht, visited him often in his house in LA. I got to know him very well and we got on very well. In the end I reported what I found, he revealed.
He said that there was enough material for a second book. Oh yes, there will be a sequel. Hell be with us for a long time I think, Bower confirmed.
On being asked whether Cowell would speak to him for the follow-up, he replied in the affirmative. I think he will. He said last night that he will, he said.
Bower said that despite building up a close relationship with the 52-year-old, he still had to dig to find out more about the women in his life.
He didnt hand it out to me. He made me go and do what journalists do, which is dig, he said.
Then I confronted him with some things - and other things I wouldnt tell him about, he said.
According to Bower Cowell came to know of the books content, was when, when he read the newspaper serialisation.
And the writer explained that he felt there were some details, which should not be included in the book.
There are a couple of things. I got so close to him there were times he would say things, do things ... we were so close I was privileged to see things.
I thought that was so private, I wouldnt abuse my facility. That was something I really shouldnt put in the book, Bower said.
I would sit with him until 3am or 4am. For example, when he said Cheryl and Dannii Minogue were his toys, he wouldnt have realised how explosive that was and I can assure you I didnt tell him. I just noted it.