The Kissing Booth stars secretly filmed third movie

Joey King and the cast of The Kissing Booth franchise secretly filmed a third instalment while shooting the sequel.

King and her co-stars Jacob Elordi and Joel Courtney took part in a live fan event on Netflix's YouTube channel on Sunday to promote The Kissing Booth 2, which premiered on the streaming service on Friday, and revealed that they shot the third film at the same time as the second.

"We filmed two and three at the exact same time," Courtney shared, according to The Hollywood Reporter, while King added, "It was the hardest secret to keep ever."

She explained that filming was tricky because "in one day we'd be filming both" and went on to thank the fans for making a third film happen.

"I want to thank the fans for their tremendous support... The explosion of love has been so real. It’s because of everyone on here that all of this has happened," King, who also produces the franchise, said.

Netflix officials confirmed the news on social media with a promo video and a clip from the forthcoming edition.

According to Deadline, Vince Marcello, who adapted and directed the 2018 original and new sequel from Beth Reekles' novels, has already finished shooting the third instalment, which is currently in post-production.

It was filmed in South Africa and the story will pick up where the sequel left off, with King's character Elle figuring out where to go to college.

"Coming to Netflix in 2021 #TheKissingBooth3. I couldn’t be happier!!!! Should Elle go to Berkeley or Harvard????????" she wrote on Instagram alongside the promo video.

Her co-stars Taylor Zakhar Perez, Maisie Richardson-Sellers, Meganne Young, and Molly Ringwald, will also be back for the third film, which debuts on Netflix in 2021.