the last function can return the value of a specified field from the last related record.
You can specify a sort order on the relationship that sorts by the date field (or a serial number field) in descending order. To define a sort order for a relationship, double click the relationship line between the two table occurrences and select the sort option for the table occurrence of the desired related table. This will affect what related record is first and which is last throughout your system so it can affect calculation results and what is shown in portals throughout your database.
You can, instead, use a one row portal with the same sort order specified for the portal instead of the relationship. This will only affect what you see on the layout where you set up the portal.