Justin Bieber came down with a severe case of amnesia when it came to Selena Gomez, 'cause he couldn't remember a damn thing about her ... or their breakfast.
Paps got Bieber in WeHo Sunday after he came face-to-face again with Selena earlier in the day -- and when asked if he and his ex were getting back together ... Justin basically hit back with the who, what, where and NO WAY routine, much to the paps' amusement.
We broke the story ... Justin sat down with Selena Sunday morning at a cafe in Westlake Village -- sans her BF, The Weeknd. It was the 3rd recent sighting of the 2 exes.
Lucky for Justin ... we got this photo of the 2 of 'em to jog his memory. Look familiar, bud?
As if this wasn't enough ... JB was later seen pulling into Selena's house on Sunday night. Apparently breakfast just wasn't gonna cut it for one day.