Later in relation to the proper time something should have happened. "Happy belated birthday!"

Is Belated an adverb?

belatedly adverb - Definition, pictures, pronunciation and usage notes | Oxford Advanced Learner's Dictionary at OxfordLearnersDictionaries.com.

Is Belated a real word?

coming or being after the customary, useful, or expected time: belated birthday greetings. late, delayed, or detained: We started the meeting without the belated representative.