Guidance with drafting letter to a biological son

About 28 years ago, I had agreed to a closed adoption for my son. At the beginning of this month, I had received my DNA results from Ancesty.com. Two years ago, my son had conducted a DNA test from Ancestry, which I didn’t know about this test. From the Ancestry DNA test, we are parent/child. Now, I have the name of my son, contact info (snail mail address), more information about adoptive parents, and photos of him from social media accounts. My intent is intro myself, confirm DNA tests, provide some biological data, and open an invitation to communicate with me further. So, do I say, “I am your father,” like Darth Vader? Like to use a bit of humor. Any guidance would be hugely helpful.