Taylor Swift was certain THIS song would hit hard on Eras tour

Taylor Swift almost had a “mental breakdown” after adding one specific song to her Eras Tour setlist, one from The Tortured Poets Department segment.

As the first two episodes of The End of an Era docuseries premiered on Friday, December 12, the multi–Grammy-winning singer was seen rehearsing her eleventh studio album.

The rehearsals took place at a "top-secret rehearsal facility" built by her team, of course.

While Swift moved across the platform of the set, she revealed a song that would make her particularly emotional.

While fine-tuning the song order for The Tortured Poets Department segment of her show, Swift could be seen singing snippets of the tracks in her rehearsal space.

After performing a bit of "Who's Afraid of Little Old Me?", she laughed, saying, "I'm gonna have a mental breakdown during this song. It's gonna be so fun."

In a voiceover, Swift explained her mindset for the Eras Tour:

"My goal was that fans wouldn’t leave feeling like they missed anything. I’ve always tried to give them something unexpected," she said.

Swift added that during the first half of the tour, audiences had no idea she was working on The Tortured Poets Department:

"In the middle of releasing the album, we had to be all hands on deck, creating a whole new 'era' to weave into the show and represent that album," she said.

The End of an Era, a six-part docuseries, now has its first two episodes streaming on Disney+.

RELATED: Taylor Swift beams with pride over fans' 'insane' move at concert