truncate a string x characters after a delimiter

hello,
i have a combobox form control that has a list of names in it in the format of "lastname, firstname" i need to convert that string to "lastname, f." for an if command that comes next. i don't know how to shorten the string correctly as the first name doesn't always start with the same letter (obviously) and the last name won't always be the same number of characters.
what i do know is the comma delimiter will always be in the same spot and the space will always be after it. also it's safe to assume there will only be 1 comma per string, and there will never be middle names or initials.

i need to put a note on my monitor so i stop forgetting about InStr. this worked perfectly thank you!