I went with my army and my sovereign to enemy territory (we are at war) , on their resource (i believe it was some shard).

I wanted to destroy it (they had a building on it) ,but did not know how, anyway, it's unrelated. The problem that after several turns I returned to my territory, my town , entered it and...

Got the message that town was conquered by the side who's territory I just visited. But there were no enemy in sight.

Somehow my sovereign and his army after a stay on enemy side of the border became enemy.

What to do with traitors like that?