Extract only the text beyond the last delimiter in a string

I am trying to extract only the text beyond the last delimiter in a string, and drop everything else.

For example:

AlphaText1:AlphaText2:AlphaText*

AlphaText1:AlphaText2:AlphaText3:AlphaText*

I only want the portion I have named AlphaText*, which may be following the 2nd, 3rd, or even 4th delimiter, which is ":".

I know I can split the data into 3, 4, or more columns, but I don't want anything but the alpha-numeric content that follows the last delimiter in the string.

Does anyone know what formula to use for this purpose?