Sub TheLetterOfTheColumn()
Dim Cell As Range
Dim ColLetter As String
Dim LigNumber As Long
Dim ColNumber As Integer
ColNumber = Cells(1, 256).End(xlToLeft).Column
LigNumber = Cells(65536, ColNumber).End(xlUp).Row
Set Cell = Cells(LigNumber, ColNumber)
ColLetter = Left(Cell.Address(False, False), (Cell.Column < 27) + 2)
MsgBox 'La Dernière Cellule de ce tableau est ' & ColLetter & LigNumber, , 'La Colonne est ' & ColLetter
'Ou encore
MsgBox 'La Dernière Cellule de ce tableau est ' & Cell.Address(0, 0)
End Sub