The epic showdown between The Beast, David Dunn, and Mr. Glass has officially begun.

On Monday, Glass, the sequel to both Unbreakable and Split, began filming in Philadelphia. “Day 1: Seventeen years in the making #Glass,” tweeted director M. Night Shyamalan.

The blending of two of Shyamalan’s most successful films was made possible by the shocking conclusion to Split, which was released earlier this year and grossed more than $275 million at the worldwide box office. Starring James McAvoy as a troubled man with 23 different personalities, the thriller ends with McAvoy’s Kevin transforming into a new identity: The Beast. But, the last shot is of Bruce Willis, reprising his role of security guard/superhero David Dunn from Shyamalan’s 2000 film Unbreakable.

The director previously broke down the twist with EW, revealing that the character of Kevin was in the original Unbreakable script and sharing his hopes to make a third film in the series. Then, in April, Shyamalan confirmed plans for his “dream” project.

Glass follows Dunn’s pursuit of Kevin’s superhuman figure The Beast, leading to the emergence of Samuel L. Jackson’s Unbreakable supervillain Mr. Glass, who holds vital secrets about both men. Split star Anya Taylor-Joy, who played Casey, Kevin’s sole surviving victim, also returns, while American Horror Story vet and Golden Globe winner Sarah Paulson is among the new additions.