Couldn't find a built in function - had to create a User Fuction for this.
'======================================
Function GetCol(ColumnNumber)
FuncRange = Cells(1, ColumnNumber).AddressLocal(False, False)
'Creates Range (defaults Row to 1) and retuns Range in xlA1 format
FuncColLength = Len(FuncRange)
'finds length of range reference
GetCol = Left(FuncRange, FuncColLength - 1)
'row always "1" therefore take 1 away from string length and you are left with column ref
End Function
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In a separate Module
Colname = GetCol(63)
Will return Colname as 'BK'