So I hooked up a good friend of mine with my old rig. We took his old drives (1x 256GB SSD for the OS and 1x 1TB HDD for data) from his old computer and put it in the new one.
We wanted to do a clean install of Windows on the SSD and I accidentally deleted the wrong drive (the HDD) while trying to delete the already existing partitions on the SSD (Here is an example(!) screenshot of the interface I am talking about, and what button I pressed)
After doing this I instantly stopped the installation and disconnected the drive from my PC (after shutting down)
Now, is there any way to get the data back to the state before the accidental deletion? My friend had about 600GB full of data and I really don't want him to lose all that.