Katy Perry, Niall Horan, MTV Video Music Awards 2012

Jeff Kravitz/FilmMagic

Katy Perry and Niall Horan's friendship is anything but hot and cold. 

As the new American Idol judge turned 33 today, an exciting new chapter in her friendship with the former One Direction member began. 

In honor of his friend's birthday, the "Slow Hands" singer took to Twitter to wish "the loveliest lady" a happy birthday and a good day, before saying "I love you."

Before you ask yourself, 'Where did this come from,' we're here to explain it all. 

The two's friendship was forged when Niall first auditioned for the X-Factor back in 2010—where Katy was a judge—and Katy made the deciding vote that allowed him to continue on to the next round.

Since his subsequent rise to fame, the stars have remained close and continued to cross paths due to their popularity in the music world. In fact, these two have built a friendship that fans simply can't get enough of. 

To see the timeline of their friendship and flirtatious encounters check out the photos below!

Katy Perry, Niall Horan, MTV Video Music Awards 2012

Photo by Kevin Winter/Getty Images

Niall Horan stole a kiss from Katy Perry... and he liked it! Following the on-stage smooch, Niall spoke in a daze about the glorious moment, saying, "I don't think there will ever be anything cooler than kissing her... until I marry her, maybe."

Niall Horan, Katy Perry, One Direction

Instagram

While walking the red carpet at the 2014 ARIA Music Awards in Australia, Katy supported her friend and even photobombed the One Direction members.

Niall Horan, Katy Perry

Instagram

The One Direction pop star cheekily captioned his photo, "She said yes," but not in the way you think! While they are unfortunately not getting married, she did technically say yes to Niall when he first auditioned for The X Factor on which she was a judge, back in 2010.

Niall Horan, Katy Perry, One Direction

Instagram

Niall's slow hands are all over "his lovely wife" Katy in this group photo with their future "groomsmen." Are we the only ones hearing wedding bells?

Niall Horan, Katy Perry

Darren Leigh Roberts/Newspix/Getty Images

The two singers performed at the finale for Australia's The Voice and were able to spend some koalaty time together down under.

Niall Horan, Katy Perry

Snapchat

Contrary to fans wishes, Katy Perry has made it clear that the two are just friends. "He's always trying to like, get my number, to like, maybe flirt with me but I'm like, 'I could babysit you. I'm like your mom!,'" she joked.  

Niall Horan, Katy Perry

Getty Images/Dave Hogan for One Love Manchester

Along with a handful of other performers, the two pals joined together to raise money for the One Love Manchester Benefit Concert hosted by Ariana Grande

Niall Horan, Katy Perry

Lester Cohen/WireImage

Despite the fact that Katy totally friend zoned our boy Niall, there is nothing but love between the two, with the former One Direction star recently tweeting, "Happy birthday to the loveliest lady @katyperry. have a good day, love you!"

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