It may have been a brief love affair but it was one that set the world on fire. Sadly, Swift's heart was left broken following the whirlwind romance.
Like many of her exes, Styles has inspired some of her music from that time in her life.
Excitement has been buzzing around the rerelease of 1989 and it appears one previously unreleased song Is It Over? has some pretty striking connections to her former flame.
We take a look at the key moments throughout 1989 that Styles has been linked to from the snowmobile incident to the infamous blue dress.
Swift said she saw her life flash before her eyes in a serious snowmobile accident with an ex-boyfriend which was always rumoured to be Styles.
Styles and Swift had gone skiing in 2012, with Justin Bieber and Selena Gomez in Utah.
In Is It Over?, the songstress sang about the incident again with the lyrics: "When you lost control / red blood, white snow."
The same accident was referenced in her 2014 song Out of the Woods with the lyrics: "Remember when you hit the brakes too soon / twenty stitches in a hospital room."
Swift revealed why the snowmobile accident - in which she said she was "not as hurt" - had remained a secret until her release of Out of the Woods.
She told Rolling Stones at the time: "You know what I’ve found works even better than an NDA? Looking someone in the eye, saying, 'Please don’t tell anyone about this.'
"People think they know the whole narrative of my life. I think maybe that line is there to remind people that there are really big things they don’t know about."
The poignant lyrics "blue dress on a boat" appear to reference when Swift was pictured looking glum after her split from Styles.
Initially the lovebirds had planned to spend New Year’s together but it didn’t go according to plan.
Instead in 2013, the Mail Online pictured Swift wearing a blue dress on a boat by herself as she left their holiday in the island of Virgin Gorda early.
This surely is the moment she is singing about?
For the Out of the Woods video, Swift styled a blue dress which at the time of its release was seen as a nod to the memorable photograph.
There remains a lot of overlap between Out of the Woods and her song from the vault Is It Over?
Also in Is It Over?, she then accused this ex of being a “lying traitor”.
She sang: "You dream of my mouth before it called you a lying traitor / You were searching every model’s bed for something greater."
Plus she accused her former flame of showing off his new girlfriends in the spotlight with the lyrics: "If she's got blue eyes, I will surmise that you'll probably date her."
It has echoes of Styles' song lyrics From the Dining Room: "Woke up the girl who looked just like you, I almost said your name."
Social media was awash with fans speculating Styles inspired Is It Over? saying: "Harry I love you so much but after hearing is it over now, I feel like I need to give you a slap."
"She is so ruthless for is it over now? Like if I was Harry Styles I would go into hiding."
"Someone check on Harry Styles after Is It Over Now?"
"Is it over now is the response to the style ft. harry style truthers."
"Harry listening to Is It Over now?"
"Is it over now? Is sooooooo explicitly about Harry Styles omg I love it."
Before the rerelease of her famed song Style, many fans thought Styles may even co-feature on the track long suspected to be about him.
Style is a song about two people who keep coming back to each other in a rollercoaster romance.
Swift has never confirmed this song was about Styles, although many people speculated it was because of the title almost being his name.
Of the title though, she once told Ryan Seacrest: "This song reminds me of driving in the middle of the night. I loved comparing the feeling that never goes out of style.
"The hook is we never go out of style. We never go out of style is a long hook."
What has Taylor Swift said about her dating history?
Swift is taking back control of her dating history.
It's no secret her love life has been tabloid fodder during her time in the limelight but Swift has hit back now and in other words she always shakes it off.
In her vulnerable new prologue, Swift has wore her heart on her sleeve when it comes to falling in love and her experiences especially when she first shot to fame.
Speaking openly about her romances, she revealed how she even swore off dating some time and appeared to shutdown the Karlie Kloss dating rumours.
She said: "If I was seen with him, it was assumed I was sleeping with him. And so, I swore off hanging out with guys. Dating, flirting, or anything that could be weaponized against me by a culture that claimed to believe in liberating women but consistently treated me with the harsh moral codes of the Victorian era...
"I swore off dating and decided to focus only on myself, my music, my growth, and my female friendships.
"If I only hung out with my female friends, people couldn't sensationalize or sexualize that right? I would learn later on that people could and people would."