In 1977, Italian horror director Dario Argento made Suspiria, which is arguably his best-known and best-loved film. In 1980, he released Inferno, which I haven't yet seen. I never realized until recently that these two films were the first and second parts of a proposed trilogy, the "Mother Trilogy." Apparently, these two ambitious, supernatural films didn't perform as well as expected and the money people encouraged Argento to go back to his simple giallo efforts. That he did, and he continued doing so for 27 years until finally he found his chance to complete his trilogy with the new Mother of Tears. Fortunately, all that time allowed his daughter Asia Argento (who was 2 years old when Suspiria was made) to grow up into a sexy actress who could star in his film.
Coincidentally, in many ways there's some similarity between Mother of Tears and Francis Ford Coppola's The Godfather Part III (1990). They both took decades to produce after the first two parts were completed in close proximity; they both come from directors of Italian descent; and they both feature the director's daughters in the third installment. They're both disappointments in comparison to the originals, but taken on their own terms, they both work remarkably well.