You obviously do not know enough about the english language to use whom correctly. Whom, in the case of the above captioned subject line, is the objective form of the word who. In this case, the OP should have used who, which, in this case, is subjective.
In other words, I AM AM HE WHO PROMISED TO RETURN
Then there is the missing word!
There should be an "AND" between return and let.
To the relatively educated english speaker, the subject line is almost as painful to read as the transcript of one of Dubya's speeches.
Therefore, the line should look like this:
I am he who promised to return and let ye know the truth.
Now I will give you my reaction: