Excel - change the last character in a cell in increasing alphabet down a column

Hi I want to change the last character in each cell in increase alphabet down a column, for example in a column I have

1234A
1234B
1234C
1234D
etc

How do I use a formula so that I can hold Ctr+Down to fill down the column while it automatically changes the last character in alphabetical order (A,B,C,D,E so on)?

Thanks!