Keys have a maximum of seven singular accidentals in their signatures, which is the case with the last sharp key, C-sharp major. But, if we continue the pattern of sharps, the next key signature would be G-sharp major, which contains an F double-sharp (see image).
G-Sharp Major’s Alter-Ego
For the sake of efficient notation, we can express the same exact scale with only four accidentals by using the key of A-flat major. This key is tonally identical (or “enharmonically equivalent”) to G♯ (compare on the keyboard in image #2).
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