Ok. No fluff. Since you are here, I assume you are clear on what you are doing and that your machine/installations is UEFI based. Let’s just hit the keyboard.

Steps

All the steps are to be followed in Windows and are same for almost every Linux distro.

Remove Bootloader/Grub

  1. Open 2 Command Prompt windows as Administrator
    1. Open Run dialog - Win+R
    2. Type cmd
    3. Press Ctrl+Shift+Enter
  2. In the first window, launch diskpart
  3. List all the disks connected to your computer with list disk command
  4. Select the appropriate disk where both your operating systems are installed along with the EFI partition with select disk <num>, where <num> is the number of the disk shown in the previous result
  5. List the partitions on the disk with list partition
  6. Select the EFI/System partition with select partition <num>
  7. Mount the partition with assign letter=x and switch to other cmd window
    1. Use some other mount point if you already use x for a drive
  8. Now, type x: and hit enter
  9. List files/folders with dir command
  10. Find a folder with name related to your distro/grub/linux.
    1. It might be in one of the sub-directories such as EFI
    2. Example: For Fedora, it might be located as X:\EFI\fedora
  11. Delete the folder with rd /s <dirname> where <dirname> is the name of your folder and close the window
  12. In the the other one, unmount the EFI partition with remove letter=x or whatever mount point you set

Reclaim Secondary OS' Partitions

  1. Open diskmgmt.msc with Run Dialog
  2. Delete the partitions you created for dual boot or the ones that were automatically created by your distro
    1. You can identify them as they are generally without labels and unrecognized by Windows
  3. Create a new NTFS partition with freed unallocated space after that

With that, you have successfully removed the secondary OS. But, not all the traces.

Remove Boot Menu Entry

  1. Launch cmd as Administrator once again
  2. List all boot menu entries with bcdedit /enum firmware
  3. Find your deleted OS' entry and copy its identifier
  4. Export the bcd store with bcdedit /export newbcd
  5. Copy for backup with copy newbcd bcdbackup
  6. Edit the exported bcd store and remove the entry with bcdedit /store newbcd /delete <identifier>, where <identifier> is the identifier you copied earlier
  7. Import the newbcd back with bcdedit /import newbcd /clean

And, now you have no traces of dual boot on your machine.

Note: I personally follow these steps, each time I get rid of a distro. This is a one-stop resource that I wish I had the first time I did it. Other websites leave out the boot-menu entry part or some other details. I will improve the guide for readability and beginner-friendliness when I get time.