Capture Just Last Name In A Cell Containing First Last And Sometimes Middle

I want to extract just the last name from a cell that contains the full name and put just the last into a seperate cell.

WHAT I AM DOING: i copy the contents of a internal screen onto a spreadsheet that i use to check various peices of info and calculations. when i save I like to save my sheet with the last name and then acct number. The internal system screen combines the customers names into a single cell. Right now i have to type the last name into a new cell and have a simple save macro that concatenates that last name with the acct number and saves it into the appropriate folder.

The field i am pulling from is always formatted with FIRST NAME then MI (IF PROVIDED) and then LAST NAME. So when i dump the screen contents into excel A20 may be MIKE SMITH, or MIKE T SMITH. so i need something that looks backwards in the cell and stops at the first space and dumps SMITH into another cell of my choosing (B1 in this case)