As far as I can tell from the video
There's a few seconds of intense fire at the front following the initial outburst, which looks a lot like the second stage motor firing against the first stage. Shortly after that you get total break-up from aerodynamic forces (which is what actually destroyed Challenger and Columbia).
(
evil_andy Stick stick stick stick sticky sticky stick stick, Sun 28 Jun 2015, 17:50,
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