Bright light (definitely NOT the ISS) observed shortly before a flyover by the ISSI went outside to observe a flyover of the ISS which was scheduled to pass almost directly overhead at 9:20pm local time from NW to SE. At approximately 9:15pm I observed a light similar in brightness to the ISS but north of my location. After observing the light for a few seconds I realised it could not be the ISS: it was flying in the wrong direction (nearly west to east) and was too far north. The light also appeared to change direction a couple of times but this may have just been an illusion created by the atmosphere.After checking the Heavens Above website, I was able to confirm the ISS was not yet visible from my location so I returned to watching the object. Soon after, I went back outside the light abruptly vanished.A few minutes later I observed another bright light NW of my location and, after watching for a short time (and checking the Heavens Above website again) I was able to confirm this second object was the ISS. I watched the ISS for several minutes until it dropped below the horizon.The unexplained light I observed was first seen roughly north of my location and was in sight for about a minute. I think it was at a very high altitide although I have no way of knowing for certain. It disappeared after travelling across about 20 degrees of the sky reaching a position roughly NE. Angle above the horizon started at about 75 degrees and finished about 60-65 degrees above the horizon.Weather at the time was moderate wind (about 25km/h) from SE. Sky was mostly clear - no clouds around where the light was observed. Many stars visible but no moon.At no point was any sound heard nor were any changes of colour or brightness noted before its disappaerence. It was a steady, bright white light.Personal info. I am a qualified educator (College/University graduate) in my early 50's. I have worked in education and security and I am a trained observer. I am a keen amateur astronomer and am fully familiar with the night sky. I know what stars, planets, the ISS and satellites look like and have observed many meteors. The object I saw resembled the ISS for brightness but was definitely not the ISS.