##R, <s>27</s> 12 bytes

**EDIT :** New version, from an excellent idea from @Jarko Dubbeldam

    LETTERS[T*T]


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Quite a funny challenge !  

Basically, this takes the `26th` element of the reversed vector containing the uppercase letters (`LETTERS`, which is a **R**'s built-in vector)

*Previous version**s*** (same number of bytes) *:* 

    L=LETTERS;rev(L)[length(L)]
    rev((L=LETTERS))[length(L)]