I'm thinking of a translation of
Let me tell you.
One thing that comes to mind is
(a) Lassen Sie mich Ihnen sagen.
but it doesn't sound quite correct. Another possibility is
(b) Lassen Sie sich gesagt werden.
(c) Lassen Sie sich gesagt sein.
both of which sound better, but might not necessarily convey the word "me" (although that should be clearly implied?) What do you think?