Billy Joel shared an update on his health nearly two months after he announced he had been diagnosed with a brain disorder.

And then Billy Joel pulled up alongside them ... Joel — who is recovering from a brain disorder known as normal pressure hydrocephalus — and his wife Alexis then posed for a selfie with the driver.

The Piano Man crooner, 76, worried fans in May when it was announced he had been diagnosed with normal pressure hydrocephalus (NPH ... and thank you for understanding." Billy's wife, Alexis Joel, 42, ...