Had to have happened... a few months over eight years ago. My mother and I were heading to a store, to pick up a few things. I don't remember the exact conversation too well, except that at one point she jokingly asked if I wanted diapers. Shocked, I said no immediately. I later asked what she'd have done if I had said yes, to which she (still jokingly) said she would've gotten them. It was dropped after that, and nothing was really thought of it until a few months later. At that time, I randomly wondered how it might actually feel to be in one again, and went so far as to sneak one out of a place that had some stray diapers and pullups laying around. That same night, I had a WTF moment and hid the thing, eventually tearing it apart to throw away. The desires didn't return until a few years later, just as randomly as before, and I ended up finding out about this whole scene. It's stuck ever since then, with my desires waning and waxing at times.
Unfortunately, I've yet to get the chance to experience a proper, adult-sized diaper, something I hope comes soon now that there is some consistency in these interests.