Historical fiction-romance “Bridgerton,” has become a worldwide phenomenon. The TV show, helmed by Shonda Rhimes, has broken Netflix viewership records. The original book series, written by Julia Quinn, has sold millions of copies.

A spinoff prequel series, titled “Queen Charlotte,” dropped on Netflix on May 4. The companion book, co-written by Quinn and Rhimes, is out today. The story follows how the marriage of Queen Charlotte — who is Black — to King George of England changed high society.

Quinn, who grew up in New England and studied art history at Harvard University, spoke with GBH News about the novel and her explosive success since the release of the Netflix show. Excerpts from the interview follow and you can hear the full interview above.

Haley Lerner: Where did the idea start for the “Queen Charlotte” book and TV projects?

Julia Quinn: It absolutely started out as a television show, which I was not directly involved in. The powers that be over at Netflix pitched it and said, we love this character, we should do a spinoff. Shonda let me know, I thought it was amazing.

And then I have to give credit where it's due. My husband immediately said, “You have to write the novel.” And I said, “Okay. I don't know. I mean, I've never done that.” He says, “No no you have to do it with Shonda as your co-writer!” So I pitched it to her as an idea at the premiere of "Bridgerton" season two in London, just literally backstage at the red carpet. I found out much later that she had the same idea and had even said to somebody, “Do you think she'd want to do it?” So we were both coming up with the same idea independently.

Lerner: How was the process of working on the book together?

Quinn: It was great. It was so smooth and easy, in part because it was really more like taking turns. She did her thing and then I did my thing. I checked with her at one point to make sure I wasn't going way off base, since the initial genesis was hers. She wrote the scripts and then I figured out how to turn those scripts into a novel.

Lerner: Are there differences between the book and the show?

Quinn: There are differences because it's a different medium. There are things that you can do in a television show that you can't do in a book and vice versa. So, for example, I was able to go into the character's heads in a way that she couldn't in the scripts, which was really fun. I was able to fill in some gaps where maybe between two episodes a few weeks have gone by.

Lerner: This book switches between multiple points of views, one being Lady Danbury who is a fan favorite in both the Bridgerton show and books. How did you go about writing these different perspectives and who was your favorite to write?

Quinn: This was the first time I'd written a book in four perspectives. All of my other books are very tightly focused on the hero and heroine.

I liked getting into the secondary characters. I really did like writing Lady Danbury a lot. She's a character who has been in my books since a book called “How to Marry a Marquis” which was released in 1999. So she actually predates the Bridgerton series.

The Lady Danbury I have written in my novels is not exactly the same as the Lady Danbury who was on the television show. The Lady Danbury in the television show is Black. She's a little bit younger than the Lady Danbury in the books. But the personality is still there. It was fun to get into her head in a way that I've never been able to and to see how she's coming about and how she is seizing her power and her agency in a time that really didn't want to let women have either of those things.

Lerner: This book deals heavily with race and takes place in a fictional timeline where Queen Charlotte is a Black woman and her marriage to King George changes the state of race for the ruling class of England. This is the world that's established in the "Bridgerton" TV show, but since this is a prequel, it’s not the world of your original books. How was this change brought up and how did you deal with writing the story?

Quinn: I really just took my cues from [Rhimes]. She's the one who wrote the original scripts. And I wanted to follow not just the depth that she wanted to go into, but also the tone. So I really let her take the wheel on that.

There were a few things I had to look into with her and check with her. So, for example how do we refer to certain groups of people in that time period? Because it is a fictional timeline, but you do want to use certain historical terms.

I had to come up with certain types of nomenclature that may not have been in the show, for example, in this London society, certain groups of people are referred to as the "dark skinned elite," and that would have been the very wealthy nonwhite members of society before Queen Charlotte's marriage. And so for things like that, I would go to her and say, “What do you think of this term? Do we think this is a way of referring to what was going on while being respectful?” You know, I don't think I would have taken on this project without Shonda as my partner, to be quite frank.

Lerner: And why is that?

Quinn: Well, she brings certain life experiences and knowledge that I just simply don't have.

Lerner: In this book, King George deals with mental illness and memory loss. How did you go about writing his character and including his condition in his love story with Queen Charlotte?

Quinn: This isn't actually the first time I have written a character who deals with mental illness. In my book “To Sir Phillip, With Love” there was a secondary character who very clearly had what we would now recognize as clinical depression. It was a big challenge to think how do I write about something that we understand so much more clearly now, and how do I write about it in a way to show how other people perceive this? And how might people who are kind, goodhearted people perceive something like this that they completely don't understand as we do?

For this, one thing that we did in the book that you don't have in the show is there's the scene where George is having one of his episodes, but you're getting it from inside his head from his point of view. So you actually get to see his thought process devolving and sort of breaking down. How tortured this was for him, not just when he's having these episodes, but even though he can't really remember them so well afterwards, he knows they're happening and he knows that they're affecting all the people around him. And he's scared because he doesn't know what's going to happen.

In any sort of romantic relationship, people have things that they fear. And he has this very real fear. You then have the character of Charlotte and how is she going to deal with this, realizing that she's falling in love with this person who has this very real affliction and it becomes something that they must overcome, but also accept.

Lerner: Overall, what do you hope people get out of the Queen Charlotte story? Both the book and TV show.

Quinn: I wanted to say something sort of kind of trite and hokey, like, oh, love conquers all. But it doesn't always. Love helps everything, and it makes everything better. But you also need to find your inner strength. And I think it's this wonderful story of love making everything in life better than it was. But, still needing to be your own person and to be strong for yourself and to be strong for the people around you.