How do I merge cells when using addRow()?

[NayeerBM]

So I need to generate an excel spreadsheet based on data from DB. Once I add in all the data from the DB I need to add in a new row at the bottom that says when the spreadsheet was generated like so:

I don't know how to get the cells to merge here, I can't use worksheet.mergeCells() since I don't know how many rows of data there will be in the DB. How would I merge the cells when using worksheet.addRow()?