What happens if there is a insurance lapse on a car that is registered to one person, but owned by another?

My ex is refusing to pay the insurance on his car. I own the car, it has a lien on it, but I just paid off the loan (which my ex does not know) and will be getting the lien off the car asap. The car is registered to him and the insurance plan is in both our names. If he does not pay the insurance and it gets cancelled, can I be penalized? Is the insurance lapse on him since the car is registered to him, or on me, since I am the main owner of the insurance policy?