Is it possible to take a string of 26 characters, A to Z, and scramble it without every repeating a character

I want to populate 26 edit boxes with the letters A to Z. Already done. Now I want to click my Scramble button and rearrange all 26 letters randomly without any letter repeating. I've tried Delphi's Random, RandomRange, RanSeed, etc and various code snippets found via google but none of them work. I'm on XE8 if that helps.