When Diana got married what did her last name change to?

The Royal Family have no need of last names as every one knows who they are , However the do actually have one. Queen Victoria's husband, Prince Albert was a member of the House Saxe-Coburg-Gotha, so all the descendant from then on carried that name. Experts started to worry and decided during the First world War that because people were starting mutter that it sounded too German, they should have an Official Last name and so the name Windsor was applied to the Family.

So Diana took the name Windsor when she married Charles, but never reverted to Spencer when she divorced