Katy Perry and Niall Horan are engaged ... but in an Instagram photo only!

Relax, relax, relax John Mayer and all the Directioners who adore N. Horan! It was a cute joke. That's all. No more. No less. It was all love, as the 'ROAR' diva and the One Direction member goofed off on social media.

Let's discuss how this happened, shall we?

Last month, Horan tweeted a proposal to Perry, asking her to marry him.

His original tweet is below. Yes, we melted.

With a public proposal like that, coming from a cutie like Niall Horan, how could Perry refuse? (Other than the fact that is loved up with Mayer!) Horan recently turned 20 and Perry crossed the 29 mark last month, so there'd be an age difference, but we are suspending disbelief for a second to say they'd make be-you-tee-full music together.

Okay, back on track.

This weekend, the good looking and talented twosome posed for a candid Insta snap, with Horan captioning it as follows: "she said yes ! It's happening! Haha."

Supa dupa cute!

See the photo of "Kiall" or "Naty" -- you pick! -- below!