general problems of the 2000 BMW 528

As I was driving my beloved 2000 BMW 528i on 11/9/2018 at 2:15 pm, on route 12 south in duck, nc, traveling at approximately 35 mph, smoke began pouring from the underside of the driver's seat. The heated seats were not turned on. No dashboard warning lights were on, except for a rear tail light indicator that had appeared within the last week. I had just driven through a rain shower, so the headlights were on, but I had turned the wipers off. I pulled the car over and immediately turned the ignition off. I got out to look under the front seat but there was nothing under the seat that was causing a problem. When I was on the phone with the 911 operator, flames started coming from under the seat. The duck nc police were on the scene almost immediately and attempted to us a fire extinguisher, but the seat kept burning. The duck nc fire department was just a few hundred yards down the road and when the arrived they filled the front seat with water. As I was clearing my possessions out of the car, I notice the headlights were still on, so I turned them off. Although the car had approximately 145,000 miles on it, I was the original owner and I had kept it in mint condition. I had a professional mechanic perform the maintenance work. In September of 2018, the battery had been replaced with a new BMW battery. Other than maintenance work, the car had never had any engine components fail or electrical issues. It was a great vehicle. Pictures of the burnt seat and the driver's side door are included.