Is there a function in Excel that will allow me to look at just the last two letters of a text string, and perform an operation based on what those letters are?

In other words, if I am in cell E12, I want to do something like this:

if [last_two_letters_C12]=ar,[append "áste" to the contents of E12],
if [last_two_letters_C12]=er,[append "íste" to the contents of E12],
if [last_two_letters_C12]=ir, [append "íste" to the contents of E12]

What I don't know how to do is parse out the last two letters of C12 to operate my if... statement.

Is there a simple way to do this? (Anybody who has had a year of high school español will know what I am trying to do here.)

tanstaafl.