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, Katy Perry, One Direction

Instagram

Niall Horan, Katy Perry

Instagram

Niall Horan, Katy Perry, One Direction

Instagram

Niall Horan, Katy Perry

Darren Leigh Roberts/Newspix/Getty Images

Niall Horan, Katy Perry

Snapchat

Niall Horan, Katy Perry

Getty Images/Dave Hogan for One Love Manchester

Niall Horan, Katy Perry

Lester Cohen/WireImage

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