To restore the
ext4 partition and its data, I thought about creating one, disk-wide ext4 partition. This allowed me to get access to the data and retrieve information about the partition with
tune2fs -l, as suggested by @thkala. This information looks very feasible and, so, unaltered.
Very interestingly, gparted is somewhat able to figure out the actual partition size as turns out from this warning it shows:
10.96 GiB of unallocated space within the partition. To grow the file system to fill the partition, select the partition and choose the menu
because 11GiB was roughly the dimension of the NTFS partition.
Notice the unused space that, IIRC, it was the space the ext4 had still free. The unallocated space gparted recognizes seems to be NTFS partition; now, how can I restore that one too, maybe by finding out where the first partition ends i.e. its total byte count?
Finally TestDisk handled that effortlessly.