Fatal stall of the Grumman G-73 Mallard

What happens in this video ?

The Grumman G-73 Mallard amphibian was about to fly a display during the City of Perth Australia Day Skyworks 2017 event, on January 26th 2017. A holding pattern was flown at an altitude of approximately 1600 feet, waiting to fly the display. During a left turn, the aircraft stalled and collided with the water. The pilot and passenger were fatally injured.