From left: Michael McKean, Harry Shearer, Christopher Guest and Rob Reiner in a scene from

Rob Reiner’s final film was a sequel to his first, and his collaborators are now in mourning.

“Spinal Tap 2: The End Continues,” released in September, was a follow-up to his first feature film — a largely improvised mockumentary about a fictional rock group known as “one of England’s loudest bands.”

This is unspeakable, the stuff of Greek tragedy.

Harry Shearer, Spinal Tap co-star

“He was a great collaborator, and when the four of us proposed ideas for the films, he was the one who wrote them on 3×5 cards, and organized them into a movie,” said Shearer, who co-wrote the Spinal Tap movies with Reiner and co-stars Michael McKean and Christopher Guest.

Shearer, Reiner and co-stars Michael McKean and Christopher Guest were credited as co-writers on the Spinal Tap movies, which were mostly improvised. Their writing process involved the four of them sitting in a room bouncing ideas off each other, with Reiner taking notes on index cards, he told CNN’s Brianna Keilar and Boris Sanchez.

“I just have this memory of us sitting together making each other laugh all the time,” Shearer said of their first collaboration.

Shearer played bassist Derek Smalls, while Guest was co-lead singer and guitarist Nigel Tufnel, who frequently clashed with longtime bandmate David St. Hubbins, played by McKean.

Reiner — who directed both films — also portrayed the fictional documentaries’ director, Marty DiBergi.

“He was, as they say in Hollywood, a mensch. A trustworthy and friendly and stable and reliable person that it was fun to be with,” Shearer said.

“There will be plenty of time later to discuss the creative lives we shared,” Guest said in a statement with his wife, Jamie Lee Curtis, “and the great political and social impact they both had on the entertainment industry, early childhood development, the fight for gay marriage and their global care for a world in crisis.”

“We have lost great friends. Please give us time to grieve,” they said.