Spain played Italy in their first match of Euro 2012. They then met them again, in the final.
This is very unlikely. For both finalists to come from the same group is very odd, because teams are seeded specifically to spread out the quality. Given that there are four teams in a group, your fellow finalist being the first team you played is even more improbable.
But it happened this year. That was unlikely, but unlikely things happen. What is really strange is that, in 2004, Greece and Portugal were in the exact same situation. Eight years ago, the previous tournament but one, the opening and closing games were between the same two sides. It was unlikely to happen once, so twice is ridiculous. That was eight years ago.
Eight years before that, in 1996, Germany and the Czech Republic played out the exact same story. I cannot express how unlikely it is for this to have happened not once, not twice, but three times, all with the same amount of time between them. Every eight years.
You can probably guess what happened in 1988. The Netherlands and the Soviet Union found themselves in the same group, and then met in the final. That's four times that the improbable has happened, almost impossible itself. Add that each instance was exactly eight years apart, with not a single exception to this rule, and it becomes almost creepy.
I will be watching Euro 2020 very closely. If this happens again, we can all but conclude that the universe has broken.