WE COULDN'T EVEN PROVE THAT IT WAS YOU, CALUM.
Oh Calum, you already remembered rule number one of taking naked pictures - which is never include your face - so why not do what every other celeb does and pull the old "it wasn't me" line?
Kudos for your honesty.
The naked photo is actually a naked Snapchat video, which the mystery recipient cruelly recorded and posted to the internet for the whole world to see.
Not cool, mystery girl - whoever you may be.
18-year-old Calum has actually dealt with this potentially humiliating moment in perhaps the coolest way possible, simply tweeting: "Least ya know what it looks like now" followed up by a more serious response of: "I'm still just a teenage kid learning from mistakes :)"
Despite the band's surprisingly chilled out reaction, their fans are absolutely furious and have since got #WeLoveYouCalum trending on Twitter just in case there was any doubt of their unwavering love for the Aussie.
Although the undeniable breach of Calum's privacy and trust is inexcusable, 5 Seconds Of Summer do have a bit of a habit of getting naked, like, all the time.
They even celebrated getting their first US number one by stripping off and sharing the evidence with the world - just not in *quite* as much detail as they share with their Snapchat friends.
And who can forget their brilliant Teen Choice Awards acceptance video? Which took place in a SHOWER.
5 Seconds Of Summer shot to fame after having the pleasure of supporting One Direction on the Australian leg of their tour last year.
Since then they have proved themselves worthy of having a humongous fanbase of their own, taking both sides of the Atlantic by storm with their hit single She Looks So Perfect, which also doubles as a mass campaign for American Apparel underwear.
Maybe next time you should keep said underwear ON, Cal.
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