For Renée Zellweger, reuniting with Colin Firth and Hugh Grant on the set of Bridget Jones: Mad About the Boy was a bittersweet experience.

At the movie’s New York City premiere on Wednesday, Feb. 12, the actress told PEOPLE in an exclusive interview that she felt a mix of emotions filming alongside her two longtime costars again for what is likely to be the final installment in the beloved franchise.

“It was both wonderful and sad,” Zellweger, 55, says, explaining, “We’ve been forging this friendship for over 25 years together. Through this journey, shared journey, Bridget Jones’ journey.”

She adds that there were some “real tears” shed when the movie wrapped, especially as Mad About the Boy seemingly marks the end to Bridget’s story, which first came to the big screen in 2001 with the original film Bridget Jones’s Diary.

“That’s what I understand. That’s what Colin said,” Zellweger replies when asked if she believes this truly is the last movie.

Firth, 64, reprises his role as Bridget’s crush-turned-husband Mark Darcy in the movie, though it’s revealed in the opening scene that his character was killed in a humanitarian mission in Sudan four years prior. Grant, meanwhile, returns as old flame Daniel Cleaver, who joins Bridget’s friends and family in their mission to help her find her spark again in the wake of Mark’s death as she navigates the grieving process and raising the couple’s two young children on her own.

Bridget also meets two potential new love interests — played by Leo Wodall and Chiwetel Ejiofor — leading to a little love triangle.

In a separate interview with PEOPLE on Feb. 12, Zellweger noted how this chapter in Bridget’s story felt much more “emotional” than the previous ones, as Bridget was still coming to terms with her husband’s tragic death.

“But the script was so beautifully written that the emotion just sneaks up on you,” she noted. “You think you’re heading in one direction that feels familiar, and then yeah, it just gets you.”

At the movie’s N.Y.C. premiere, Bridget Jones author Helen Fielding addressed fans’ dismay over Mark’s death, admitting she still feels guilty for “killing” him off. “I didn’t mean to and he’s actually still alive,” she jokes to PEOPLE.

“It was just the character that was killed, and it wasn’t my fault really. It was just what happened in the story,” she adds.

Fielding, 66, also shared how Zellweger and Grant, 64, portray their characters so wholly and vibrantly that she now has the pair in her mind when she writes the books.

“They’ve all got completely jumbled up together,” she says of the stars and their personas. “I’m really fond of all of them. And when I write Bridget now, I write for Renée.”