I added a second Linux Distro to my system. Ran the sudo update-grub, it found the second system and set up a boot menu for me to choose which system to boot from. All was fine.
When I was finished testing the second Linux system, I deleted the partition.
I then ran apt-update grub again, thinking it would remove this system from the boot menu.
Instead my system now boots to Grub>
After trying to fix the problem by doing Clonezilla restore, I gave up and just re-install Linux from the Distro USB. So, I can not try any suggestions but would like to hear what you think I did wrong -or
what I should have done to remove dual boot.