Condensing Taylor Swift’s extensive discography into a single concert setlist was already a formidable task. The challenge escalated when she decided to integrate a new era into her lineup, all while in the midst of her tour.

Her latest Disney+ docuseries, “The End of an Era,” provides an inside look at how Swift and her Eras Tour team seamlessly incorporated a new segment called the “Tortured Poets Department.” This addition was made during a brief two-month hiatus between performances in Singapore and Paris.

“After the first leg of the tour, unbeknownst to fans, I was crafting an entirely new album, ‘The Tortured Poets Department,’ right in the middle of its release,” shared the “Opalite” singer. “It required a full team effort to introduce a brand new era into the show, ensuring the album was well-represented.”

Swift described their intensive rehearsals, conducted in a “top secret facility,” where they meticulously fine-tuned the setlist.

Footage from the series captures Swift and her band rehearsing tracks from “Tortured Poets” at the Paris La Défense Arena. This preparation was done in utter silence to prevent any spoilers from reaching the throngs of fans eagerly waiting outside, just before the album’s April 2024 release, slightly over a year after the tour had begun.

Swift’s instrumentalists are shown playing unplugged instruments and wearing headphones in order to practice the new tunes, with the superstar’s longtime bassist, Amos Heller, even rehearsing in a shower.

“We put together all new choreography, all just hearing it in our heads because they can’t play the music on speakers because it’s not out yet,” the Grammy winner explained. “There is an entirely new order of the chapters so I am relearning the entire show, essentially.”

Swift added, “That was a risk, it could’ve gone so bad. I swear to God, if I heard people online being like, ‘I miss the old show,’ I was going to be like, ‘Oh my God, you have no idea how hard this was to do.’”

“I love having a good secret,” Swift, 35, quips in the doc. “It was such a dynamic new addition to the show.”

The “Lover” songstress’s record-breaking tour ran from March 2023 through December 2024, and blew fans away with surprise songs and guests.

The 3.5-hour show featured hit songs from nearly all of the pop star’s albums, from 2008’s “Fearless” to 2022’s “Midnights.”

One of the “Tortured Poets Department” tracks Swift opted to incorporate into her setlist was “So High School” — an ode to her now-fiancé, Travis Kelce.

Swift sent fans into a frenzy when she first performed the song at her Paris tour stop and choreographed her own version of the Kansas City Chiefs’ dance to “Swag Surfin’” by Fast Life Yungstaz.

Then, in June 2024, the Grammy winner brought Kelce out on stage during her “I Can Do It With a Broken Heart” transition on the third night of her London tour stop.

Surprise Eras Tour guests also included Swift’s longtime collaborator and friend Jack Antonoff.

The record producer shared the stage with the pop icon to perform her 2017 “Reputation” album track “Getaway Car” at MetLife Stadium in New Jersey in May 2023.

And Sabrina Carpenter, who opened for Swift at the start of the tour, returned to the Eras Tour in October 2024 to perform a mashup incorporating two of her hits — “Espresso” and “Please Please Please” — along with Swift’s 2023 track “Is It Over Now?”

Florence Welch and Ed Sheeran — who are featured in the new docuseries — as well as Marcus Mumford, Aaron Dessner, Phoebe Bridgers, Ice Spice and Maren Morris also joined Swift onstage.