get last word in string for Sonos Player

I have a string heard by HS via Alexa. I would like to get the last word from the string so I can change Sonos Play

For example the script gets this parm passed to it:

run living room stop

How do I get the STOP on the end?

I would normally look for instrrev and find the last space and then use substr to
get the last word. I didnt find any reference in the PDF for this.

Thank you