Man, if you have a healthy Regal that is eating I would not add anything that even resembles competition in with it. The dwarf will probably not do anything to your Regal, but Regals can be so temperamental that you don’t know how it will react with the introduction of another member of the same family. If it were me, I would not temp fate. You are fortunate to have such a difficult fish. It speaks VOLUMES about your care and feeding.
Congratulations man!!!!