As dawn breaks, the Second Sun rises first, and thus is brighter. Both cast reflections on the water. Intense light can be seen from two sources, and the Second Sun passes behind a cloud, proving it is not a reflection within the camera.
Then, as both suns continue to rise, the Sun becomes brighter, and the Second Sun begins to be lost in its glare. The Sun is also casting the strong reflection on the water at this point.
As this process continues, only the Sun can be seen, the Second Sun lost in its glare. Intense light is only coming from one source, the Sun source.
However, the reflection on the water still leaves a hint of the Second Sun!