Find position of last alphabetic letter in a cell

[anglais428]

I am looking for a formula that will identify the position of the last letter in a cell, ignoring punctuation and special characters.
E.g. If the text in a cell is:
This,text,in,a,cell,,,,,,
The result should be 19 as the last "L" is in position 19. It should ignore all the commas at the end.

 

[sandy666]

if result is ok, you can use Power Query (Get&Transform)

// Table1
let
    Source = Excel.CurrentWorkbook(){[Name="Table1"]}[Content],
    Replace = Table.ReplaceValue(Source,"...","###",Replacer.ReplaceText,{"Raw"}),
    LastChar = Table.TransformColumns(Table.AddColumn(Replace, "Text", each Text.Select([Raw],{"a".."z","A".."Z"})), {{"Text", each Text.End(_, 1), type text}}),
    Position = Table.SelectColumns(Table.AddColumn(LastChar, "Position", each Text.PositionOf([Raw], [Text], Occurrence.Last)+1),{"Text", "Position"})
in
    Position