He just started telling us when he needed to use the toilet, every single time. We were usually a couple of seconds late, so his diaper was still getting damp, but mostly everything ended up where it was supposed to.
We switched his diapers out for underwear, and had a day where he would start to pee, then run through the house to his toilet, desperate not to pee in his underwear (combined with asking in time. So we went through 5-6 pairs of underwear in a day). There were a couple of unfortunate poops.
Since then, he's had 3 accidents in 4 days, all of which were the same sort of Oh God, I'm peeing moments, followed by him running right away to the toilet. He hasn't had another poop accident during those days, and has woken up dry every morning (twice he woke us up in the night to use the toilet, twice we've been out of the house when he's said he had to go, he didn't like the public toilet available and he held it until we got home).
I'm flabbergasted. It was really like a switch flipped and he decided he was going to use the toilet from now on. He doesn't have an issue wearing diapers (he still wears them to bed and when we go out), just prefers to use the toilet. Would that the hobgoblin will do as well.
Of course, the latest accident - which happened just as I was thinking to myself that I could start to refer to the monster as toilet trained - happened all over my feet, a few minutes ago. So I guess I shouldn't get too far ahead of myself.