Diplo made some tongue-in-cheek claims over the weekend that he dated Justin Trudeau -- and he kept the joke rolling with an IG selfie Monday, cozying up with the politician ... and his actual ex-GF Katy Perry !

Check it out -- the DJ posted a shot with Canada’s ex-PM, both pulling shocked faces for the camera ... with Katy in the background, totally unaware she was photobombing their little moment.

Diplo captioned the pic "the one that got away" ... a cheeky nod to Katy’s hit song and their brief fling back in 2014. Play video content

Of course, just to be clear -- Diplo’s "I dated Justin" claim is highly unlikely, considering Trudeau was married to Sophie Grégoire from 2005 until their 2023 split. Play video content

As we first reported, Justin’s moved on with Kat

See Full Page