I noticed that as soon as I saw the second screen you posted and had to wonder if the D volume information was still being maintained while the partition was already removed suggesting a corrupted Partition Table. That would what the DM is actually seeing not any actual partition showing how vulnerable resizing OS partitions can be at times.
In the past I have run into some mishaps when deleting the the temp 7 RC install back then for a second resize of the XP primary in one example where the XP install disappeared! That's when Dr. "data rescue" had to be called in fast!
Somehow the D volume saw a change to extended if not an extended type partition already rather then total removal if the PT is found to be intact where it seems to have been mounted as a virtual drive explaining why it is still being seen. Or the DM has a registry error is cloning C as a D volume as far as what the DM is seeing while no actual partition is present.
W7 Ultimate x64/W10 Pro x64/W11 Pro Triple Boot - Main PC W7 Remote PC Micro ATX W7 Pro x64/W11 Pro
CPU
AMD Phenom II X4 975 Deneb 3.6ghz - 965 2nd remote pc
Motherboard
Gigabyte GA-790XTA-UD4-Gigabyte GA-880GM-D2H remote pc
Memory
Kingston Hyper X DDR3 1600 1.5v 16gb - Hyper X Fury 8gb 2nd
Graphics Card(s)
MSI HD Radeon 5750 1gb - MSI HD Radeon 6450 on mini tower
Sound Card
Creative Labs X-Fi Xtreme Audio P - Realtek onooard 2nd case
Monitor(s) Displays
ASUS VW199T-P 19" HP 2082a Main-HP 2082a 20" remote pc
Screen Resolution
Asus 1440x900 - HP 1600x900
Hard Drives
WD Black 1TB HD per OS W7, W10, and pending W11 presently on 500gb OS Drive - Pending Triple 1TB HDs for Spanned Storage/backup volume
Single 2TB external USB enclosure, single 1TB System 7 Host/Boot drive, Pending 8TB external HD for system image b
PSU
Corsair 750TX - primary / Corsair CX600 - second
Case
Antec 900-2 - SSD compatible / NZXT Vulcan mini tower
For simply unplugging any drive you first turn the system off completely and open the case up. On many cases that would be unfastening the side cover if a custom build. For an OEM premade system that will vary upon make and model as to how it was put together.
As for Disk 1 that would be D which wouldn't be a physical drive to start with since it was on the same drive as C your OS primary. The FreeAgent would be the external Seagate drive you have there which you would simply unplug from the usb port after a right click on the Safety Remove icon in the System notification area. From there you simply restart the system and go back into the Disk Management for another look.
W7 Ultimate x64/W10 Pro x64/W11 Pro Triple Boot - Main PC W7 Remote PC Micro ATX W7 Pro x64/W11 Pro
CPU
AMD Phenom II X4 975 Deneb 3.6ghz - 965 2nd remote pc
Motherboard
Gigabyte GA-790XTA-UD4-Gigabyte GA-880GM-D2H remote pc
Memory
Kingston Hyper X DDR3 1600 1.5v 16gb - Hyper X Fury 8gb 2nd
Graphics Card(s)
MSI HD Radeon 5750 1gb - MSI HD Radeon 6450 on mini tower
Sound Card
Creative Labs X-Fi Xtreme Audio P - Realtek onooard 2nd case
Monitor(s) Displays
ASUS VW199T-P 19" HP 2082a Main-HP 2082a 20" remote pc
Screen Resolution
Asus 1440x900 - HP 1600x900
Hard Drives
WD Black 1TB HD per OS W7, W10, and pending W11 presently on 500gb OS Drive - Pending Triple 1TB HDs for Spanned Storage/backup volume
Single 2TB external USB enclosure, single 1TB System 7 Host/Boot drive, Pending 8TB external HD for system image b
PSU
Corsair 750TX - primary / Corsair CX600 - second
Case
Antec 900-2 - SSD compatible / NZXT Vulcan mini tower
Was there actually any VHD created or simply a need to reboot and rescan? once the external drive is unplugged that is. Is there was an actual clone in VHD form simply locating and deleting the "D.vhd" file will see it gone.
Not finding any vhd file on the other hand would mean a totally different problem like the System Volume?PT information being corrupted somehow fooling the DM into listing a non existent drive.
If you haven't restarted the system at all since and if you went through the DM to delete the D partition and resize of C that may explain why D is still being seen where the restart would seem to be the option to refresh everything. Without the external drive plugged in Windows would then be forced to freshly detect the main internal drive by itself.
If you still end up seeing a phantom D drive afterwards then it might be time to consider a new approach following a total wipe which would be the last resort option to work with a totally new primary and Partition Table in order to clean this up for you.
W7 Ultimate x64/W10 Pro x64/W11 Pro Triple Boot - Main PC W7 Remote PC Micro ATX W7 Pro x64/W11 Pro
CPU
AMD Phenom II X4 975 Deneb 3.6ghz - 965 2nd remote pc
Motherboard
Gigabyte GA-790XTA-UD4-Gigabyte GA-880GM-D2H remote pc
Memory
Kingston Hyper X DDR3 1600 1.5v 16gb - Hyper X Fury 8gb 2nd
Graphics Card(s)
MSI HD Radeon 5750 1gb - MSI HD Radeon 6450 on mini tower
Sound Card
Creative Labs X-Fi Xtreme Audio P - Realtek onooard 2nd case
Monitor(s) Displays
ASUS VW199T-P 19" HP 2082a Main-HP 2082a 20" remote pc
Screen Resolution
Asus 1440x900 - HP 1600x900
Hard Drives
WD Black 1TB HD per OS W7, W10, and pending W11 presently on 500gb OS Drive - Pending Triple 1TB HDs for Spanned Storage/backup volume
Single 2TB external USB enclosure, single 1TB System 7 Host/Boot drive, Pending 8TB external HD for system image b
PSU
Corsair 750TX - primary / Corsair CX600 - second
Case
Antec 900-2 - SSD compatible / NZXT Vulcan mini tower
Give that a try! powerpca If the D disappears right away you will know there's a vhd on the drive somewhere you can simply delete after and be all set if no other problems appear.
Another option if that fails to work would be booting up from the 7 dvd to the Repair tools opting for the command prompt option thus removing Windows from the equation to boot live. With the external left unplugged you can run the Disk Part tool there free of anything interfering. Here's how the commands would go.
list disk (lists all hard drives, external as well as internal, any usb flash drives or memory cards if present)
select disk 0 (would be the only physical hard drive present)
list volume (will reveal all partitions present on the drive)
select volume #1 (C would be #0)
delete volume #1
exit (exit Disk Part to reboot)
If for some reason a clone of C was seen and listed as D without any substance you wouldn't see anything more then the one main volume while booting live. If you are reaching the point where a drive wipe is the only option left for a brand new primary we can take you through the wipe and new primary rather fast here.
Once you have selected the drive Disk #0 rather then using the commands to delete one volume at a time you would simply use the Clean or Clean All command as long as no other drive(the external HD) was present to wipe everything. Then you can opt to create the new primary there or watch as the 7 installer creates the 100mb System Reserved partition use for the BCD store and boot files only at the front of the drive.
Some people would rather lay claim on that small amount of drive space and simply prefer to create a new primary first before running the Windows installer. The commands would go as:
List Disk
Select Disk 0
clean all (insures a total wipe)
create partition primary
format fs=ntfs
exit
Once that is all set you restart to again boot from the 7 dvd still in the drive to run the 7 install. As long as all of your files have already been backed up you will be installing updates and device drivers some 20 minutes later on a clean install as well as brand new primary without errors.
This is of course still the last resort but insures the best results if no other solution is found to work like finding no vhd and still being plagued by a phantom D drive.
W7 Ultimate x64/W10 Pro x64/W11 Pro Triple Boot - Main PC W7 Remote PC Micro ATX W7 Pro x64/W11 Pro
CPU
AMD Phenom II X4 975 Deneb 3.6ghz - 965 2nd remote pc
Motherboard
Gigabyte GA-790XTA-UD4-Gigabyte GA-880GM-D2H remote pc
Memory
Kingston Hyper X DDR3 1600 1.5v 16gb - Hyper X Fury 8gb 2nd
Graphics Card(s)
MSI HD Radeon 5750 1gb - MSI HD Radeon 6450 on mini tower
Sound Card
Creative Labs X-Fi Xtreme Audio P - Realtek onooard 2nd case
Monitor(s) Displays
ASUS VW199T-P 19" HP 2082a Main-HP 2082a 20" remote pc
Screen Resolution
Asus 1440x900 - HP 1600x900
Hard Drives
WD Black 1TB HD per OS W7, W10, and pending W11 presently on 500gb OS Drive - Pending Triple 1TB HDs for Spanned Storage/backup volume
Single 2TB external USB enclosure, single 1TB System 7 Host/Boot drive, Pending 8TB external HD for system image b
PSU
Corsair 750TX - primary / Corsair CX600 - second
Case
Antec 900-2 - SSD compatible / NZXT Vulcan mini tower