‘Bridgerton’ author Julia Quinn: Why Penelope and Colin’s Season 3 was the ‘hardest to plot’

She’s the real Lady Whistledown.

Julia Quinn, the author of the “Bridgerton” books that the hit Netflix series is based on, said that she’s surprised by the “hugeness” of the show’s success.

“I never thought it was going to flop, because I knew what incredible production values were going into it … And I knew that it was something that lots of people wanted and wasn’t out there. I think it was plugging up a hole in television,” she added, referring to the lack of romances onscreen.

“But I did not expect it to be as crazy big as it is,” she told The Post, while promoting her partnership with International Delight (for the brand’s limited-edition Bridgerton-inspired creamers and iced coffee. The brand also had a “Coffee & Courting” dating event on February 22 in Manhattan, ahead of Season 3).

“It took everyone by surprise, in the best possible way,” said Quinn, referring to how “Bridgerton” regularly tops the streaming rankings.

Both Season 1 and Season 2 are on Netflix’s Top 10 most popular shows list, and Season 2 broke a record for most-viewed English Language TV series, with 571.76 million hours viewed in its first week.

Each season of “Bridgerton” follows a different member of the titular family as they find love in Regency-era London – all while a “Gossip Girl” like figure, Lady Whistledown, chronicles everyone’s secrets.

Season 3 (premiering Thursday) follows the story of Colin Bridgerton (Luke Newton), and his friend Penelope Featherington (Coughlan), who has a crush on him but overheard him cruelly dismissing the idea of courting her in Season 2.

“For me, the most exciting thing is that this season – unlike most ones we’ve had before and probably mostly ones that would come after – is about two characters that we already know quite well,” said Quinn.

“And so, I just think there’s a different type of emotional investment coming into it. It’s interesting because when I was writing the books – this book, ‘Romancing Mr. Bridgerton,’ which is actually the fourth in the series, was the hardest one to plot. And that’s because it had two very established characters. I usually maybe have one character you’re bringing in from before, and then you can mold the other one into what you need.”

She added, “And so this time … it was really hard to come up with a plot that actually worked for everything. I’d already made these characters with the experiences that they had.”

Each season of “Bridgerton” makes changes from the novels. For example, the Season 2 heroine, Kate Sharma (Simone Ashley), was Indian in the show, but she was white in the books, with the last name of Sheffield.

“I really think that people could look at ‘Bridgerton’ as a masterclass in adaptation,” said Quinn.

“Because each season doesn’t follow [the books] word for word. And there are things that are changed in the plot. But, if you look over the arc of the whole season, the characters are absolutely true to who they are. The main conflict is actually true to what it was. So, I think it’s really brilliant. Most of the time, it wasn’t that I was nervous about [changes]. But like, for example, I knew before they announced it that for Season 2, that the Sheffields would become the Sharmas and they were coming from India. I didn’t necessarily know how they were going to pull it off, but I thought it was a fabulous idea. So it’s not so much [about] being concerned. It is sort of being like, ‘Well, I wonder how they’re going to do that, but we’ll see!’”

Season 3 has one big casting change, in the form of Francesca Bridgerton. Previously, she was played by actress Ruby Stokes, but in Season 3, she’s played by Hannah Dodd.

“Everybody loved Rudy Stokes, but she’s the lead in another Netflix show, and she just didn’t have the time to do both,” said Quinn.

“I will say Hannah Dodd, who now plays her … the way she moves and carries herself is really reminiscent of Phoebe Dynevor. You would really believe that they’re sisters. Their characters are very different, but just the way they move is very similar, it’s cool.”

Quinn said that she often gets asked if the characters onscreen look how she envisioned them.

“I’m not a very visual person,” she said. “I didn’t really imagine them physically [before the show]. I don’t usually reread my books, but I had to go back and look through them to put together this collection that we had called ‘The Wit and Wisdom of Bridgerton.’”

She added, “And, as I was looking at them, I was seeing the actors. Now, they fully inhabit [the characters]. It’s really quite remarkable.”