To add a relative URL to a different port number in a hyperlink with HTML, you can simply specify the port number along with the relative path in the href attribute of the <a> tag.

To do this, we write:

<a href="http://example.com:8080/relative/path">Link to Different Port</a>

In this example, http://example.com:8080 is the base URL with the different port number (8080).

/relative/path is the relative path that you want to navigate to within the specified port.

Replace example.com with your actual domain name and 8080 with the desired port number.

The relative URL /relative/path can be replaced with your specific relative path as needed.

This hyperlink will navigate to the specified relative path on the specified port when clicked.