Yes, when you have one corner twisted, one will always be twisted, but it doesn't matter which one. Think of it this way: on a solved cube, each corner can be twisted in 3 possible ways, one solved, one clockwise, and one counterclockwise. Take a solved cube and twist all or most of the corners. Set each solved corner equal to 0, each clockwise one equal to 1, and each counterclockwise one equal to 2. Then add up all the values of all eight corners on the cube. If your cube is solvable, the amount of twisted corners will always be a multiple of 3. If it's unsolvable, no matter what you do to it afterwards, it will always have the same remainder after dividing by 3. So once you find out if it's solvable or unsolvable, try to solve it. You can always reduce a corner-twisted cube down to one unsolved corner, but it can be any of the eight corners. Once you get to this point, if it's unsolved with one corner twisted, check if it's clockwise or counterclockwise. The corresponding number to whatever it is will be your remainder that you got from earlier.
If you'd rather picture it in another way, twist one corner clockwise, then with that corner in the up-front-right position, do the algorithm: R' D' R D R' D' R D U D' R' D R D' R' D R U'
You'll end up with another corner twisted in the same direction.[/
I found that my brother twisted a corner... thanks tho
