If your relationship is unsorted (the default option), then the most recent related record is the Last related record:
If [ Not Isempty ( RelatedTable::neveremptyfield ) //make sure that at least one related record exists ]
Go To Related Record [Show only related records; From table: RelatedTable; Using layout: "RelatedTable" (RelatedTable) ]
Go To Record/Request/Page [Last]
Go to Layout [Original Layout]
Thanks, the duplicate will have a different serial number, correct? Basically, I'm adding a new record but copying everything from the last record.
If the serial number is an auto-entered serial number, yes. If you have a portal to the related table, you'll see a new duplicate row appear in your portal each time you run this script.