The book contrived to be simultaneously lurid and dull. Nothing. Happens. I mean really, endless iterations of "the boy", of "I don't know", of Henry being by turns an idiot, a boor, delusional, terrified mean spirited, and spiteful. Gregory loathes the Tudors but had the problem that evidence points to Elizabeth being at the very least content with her husband, so Gregory throws in a truly bizarre few pages of her falling in love with him (complete with toe curlingly bad sex scene); but then she has to fall out of love with him again and sigh resignedly in her superior Yorkly way.
She ends the book before the death of Arthur, an event that unequivocally demonstrates the couple's concern and support for one another, because how would she spin that?
So this show had a problem; the book would make terrible television and Henry would be completely unsympathetic. They chose instead to go with a romance, but there's no drama in that.