How to create related Private ticket which should visible to only internal teams not in portal

[Research]

Hi 

How can we create a related private ticket Like (Incident or case or Task) should and visible to clients on portal. 
Ticket should only visible to internal teams not flowing to portal.

Please guide me

Thanks.

[Christopher Sik · Accepted solution]

Cases are designed to be customer-facing records. Any records created under a case like Incident or Case Tasks should generally list the agent assigned to the case in the caller field. This way the customer is never aware that these records exist. Any sub-record details that the agent feels the customer should know about can then be summarized in comments at the case level.