A precedent in British peerage law has decided centuries ago that the monarch cannot hold a title from himself. This means a purely English title (and now Scottish, too). However, nothing apparently prevents from holding a foreign title, or a sovereign title. Defender of Faith can be seen as a sovereign title. Queen of dominions beyond sea is sovereign. Lord of Ireland apparently was sovereign.   Empress of India was sovereign. Man is sovereign or Norwegian. Normandy was French. Orange was Holy Roman Empire's. Hanover also. Etc.