What is the difference between Megalomania and Narcissism? As far as I can tell, both megalomania and narcissism are found in [delusions of] grandiosity. Perhaps megalomania has more focus on power, rather than just being well liked?

What is the primary difference between the two?

Are all megalomaniacs narcissists? Or all narcissists megalomaniacs? Or are they completely separate?
The DSM (Diagnostic and Statistical Manual of Mental Disorders) doesn't distinguish between megalomania and narcissism. The most recent edition of the DSM (DSM-5) classifies both as a form of narcissistic personality disorder.