This is probably emotional. Since he was already dry at night, there is no reason to suspect physical problem. I would seek advice about emotional causes. Dr. Aldort helped me alot with this kind of stuff and she works by phone internationally.

Meanwhile, he should have no choice by to wear pull ons.
Tell him it is better. Release him from the need to have a dry bed. Tell him it is normal for his age and there is no rush. The pressure to "perform" dry night is very stressful and harmful. Just let go of the whole expectation and put those pull ons back on. In the morning take them off matter of factly with a hug and a kiss. No problem.