Drama in my Absence?

Look what I found after I came home from the office. A huge mess on the balcony and this nest sitting in between.

Way up above the balcony there has been a (blackbirds) nest for many years already. They use it over and over again, I read that's not very common, but they do.
Last year it already looked like it may come down any time, sitting right on the edge of the roof beam.
Imagine my surprise when I looked up and said nest was still sitting there on the edge!
So this one is the semi-detachted house they built last year; the one I could barely see from underneath. Looked like one. Wasn't one!

But why did it come down? There was no wind today. A fight between the birds? Or only getting rid of one nest that was in the way or not needed anymore? But why not kick down the older one?

And to me, the big question: Is there someone living in the remaining nest already? Who? The pigeons I've seen come and go or the blackbirds that built it and are around as well? I really do hope it's the blackbirds. One year I had pigeons up there and the mess on the balcony was beyond description. I put up a huge sunshade right underneath and that did barely help. The sunshade had to be thrown away; it was covered with pigeon droppings several centimeters. Igitt - Yuck! Spending time on the balcony wasn't much fun that year; underneath a layer of birdpoo.

I know some of you do not understand, but I can't allow the pigeons to breed up there again. I can not use the balcony if they do and I don't have a garden. There are so many trees right around us, they really don't need to choose the nest the blackbirds built. I will watch closely. The blackbirds have never been a problem.

Here (in the extra) the nest(s) from underneath.

19:10; 9°C