After expanding VHD drives in Hyper-V, the unallocated space may be separated by other partitions.

Free space is separated by other partitions. This makes it impossible to extend the partition we want (C:).

1. Select the small partition that is between the partitions.
2. Right-click and select "Move/Size."
3. Add the total unallocated space into the "Free space preceding" section. This moves the unallocated.

This can be seen here:

Apply the configuration, then reboot, remembering to eject the ISO.