Selena Gomez dropped her new single 'Feel Me' on Friday --- a song she debuted four years ago during her Revival tour.

Selena decided to surprise fans on Friday by releasing a track about the height of her on-off period with Yummy singer Justin Bieber.

2016 was a particularly messy time for the former couple. It was the year #SelenaEndedJustinParty trended on Instagram after the then-couple fought in the comments section of Bieber's photo with ex-girlfriend Sophia Richie. It was also the year Gomez publicly accused Bieber of cheating.

Justin and Selena
Justin and Selena at the 2011 American Music Awards Reuters/Danny Moloshok

Gomez and Justin first went public with their relationship at the Vanity Fair Oscars Party in February 2011. Gomez also opened up to Seventeen about their relationship after months of avoiding the subject.

The pair broke up several times during their 10-year relationship.

Their relationship was not without controversy --- from Bieber's scuffle with Orlando Bloom in 2014, Selena's crumpling of a fan sign during her Revival tour in 2016, their memorable feud on Instagram's comment section, and Gomez's mom unfollowing her daughter in 2017.

Selena and Justin weren't officially dating in 2016 when she sang 'Feel Me' for the first time on stage. She said she wrote the track 'Feel Me' one night when she was "really irritated". The lyrics were a reflection of her state of mind when Justin was dating his now-wife Hailey Baldwin and Sofia Richie.

Gomez told fans on Twitter in January that 'Feel Me' was a reflection of who she was, not who she is. She said she left 'Feel Me' off of her latest album Rare because it "doesn't fit where I am right now."

She caved in, however, after fans kept requesting her to release the track. On her Instagram, she explained, "On the Revival Tour, I introduced a song that you guys haven't stopped talking about since. So you asked and I listened Today, Feel Me is out online and vinyl everywhere."

Her new song includes lyrics like, 'Every time your lips touch another/I want you to feel me/I want you to feel me/ Every time you dance with somebody/I want you to feel me/I want you to feel me'

Selena Gomez debuted her newest album 'Rare' which hit the top of Billboard 200 after a stiff race with rapper Roddy Ricch's two-cheek chart-topper Please Excuse Me For Being Antisocial.

Rare is Selena Gomez's first album in four years, following her battle with Lupus, a kidney transplant, depression, and anxiety.

Speaking with NPR, Gomez described her new album as a "respectful closure", and a "way to claim my story."

Gomez also described her song 'Lose You To Love Me' as a "song that is saying --- I had something beautiful and I would never deny that it wasn't that. It was very difficult and I'm happy it's over."

Gomez also shared on her struggles with mental health

"Taking care of mental health - that's forever. That's something I will have to continue to work on. Yes, I don't think I just magically feel better. I have days where it is hard for me to get out of bed, or I have major anxiety attacks. All of that still happens," she said. "As I grew up in this chaotic space, I did have to learn how to be tough, and to be strong, but I'm not this hard person.

But the way I find these moments in my life that are pretty difficult, I think the only way it's helped me is that I can use that for good."