The core has been lost, according to the technical stream:
If you wait until ~38 min and 30 seconds, the announcer says "We lost the center core".
Now to wait forUpdate:
Elon Musk has confirmed that the engineers to figure out why.center core didn't make it. To paraphrase from the SpaceX post-launch news conference
The center core obviously didn't land on the droneship, or we would have shown that... It ran out of propellant to relight the engines... It was the center one [that ignited], I believe, and the outer two did not, and that was not enough to slow it down. [something I can't make out] hit the water at three hundred miles an hour and took out two of the engines on the droneship... That sounds like some pretty fun footage, so if the cameras didn't get blown up as well, then we'll put that on a blooper reel
That was ~41 minutes into the video, I believe.