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What is the correct way to make a possessive that would mean the following:

The cat belongs to Will Anderson Jr.
Comments 
I would say Will Anderson Jr.'s. And I suppose it would be written as such, as well.
There would be a comma after the last name and before the rank, e.g., Martin Luther King, Jr.'s.
AnonymousThere would be a comma after the last name and before the rank, e.g., Martin Luther King, Jr.'s.
No
That is exactly what I am trying to type, but it comes up as incorrect on spell/grammar check.
Anonymousbut it comes up as incorrect on spell/grammar check.
Computerized grammar/spelling checkers are not perfect.

This phrase passes spell checkers in both Google and MS Word
John J. Smith Jr.'s coat