Just an Heir (the story of Michael and Kristine) is the main book, and A Silent Lover is its prequel, which centers Kristine's parents as the main characters.
27-year old Michael Keaton van Alstine was the CEO and owner of his family's conglomerate, the Van Alstine Incorporation. He may be rich, but he was not usually the ladies' man, a flaw that caused his dad to arrange a marriage to a family friend.
Kristine-Victoria Mercedez just graduated as a lawyer, but never finished her master's degree. Her twin, Gretchen-Katrina, who was almost getting married to her boyfriend, Javier, was supposed to marry Michael van Alstine, but the first meeting made Gretchen rebel against the idea.
Instead, Kristine married the man who only wanted an heir to his business. However, his mysterious personality captivated her, convincing her that the marriage won't be that bad if she will do something, even though both of them were opposites in terms of appearance of personality.
It was not just an heir.
The events in this book are fictional, even the companies that exist mentioned. However, some places mentioned really exist. Also, most of the chapters in this story are unedited, so please ignore the errors.
There is mention of characters from "Becoming a Billionaire", a Korean drama from MBC, starring Lee Bo-young and Ji Hyun-woo.