When I arrived there were workers and camera crews on the bridge, all very busy doing 'something?'.
I didn't have to wait long to find out what they were up to, I'd just chose a good spot when these dazzling spotlights sprung to life.
Beams of light swooping and cutting through the night sky, pausing for a moment, then off again in a repeating pattern.
I timed my shot to the pauses and caught this once in a lifetime image.
Then, within minutes, other lights popped up and a neon-lit speedboat burst through the scene, whizzed under the bridge, headed down-river.
Then just as promptly as they came to life, the lights were out and it was business as usual.
When I later watched the opening ceremony for the games, I saw that David Beckham had made his way to the Olympic park in a neon-lit speedboat... so that is the boat I saw... that is why they briefly lit Tower Bridge lit up this way that night.