This but unironically. African-American genetics have got considerable Caucasian admixture from all those slaveowners carrying on affairs with their slaves, like 24% white ancestry from the last study I saw on the subject (from 2015). Meanwhile the Greek Ptolemaic dynasty took up the Egyptian tradition of brother-sister inbreeding, and only occasionally branched out to intermarry with their Greco-Persian Seleucid neighbors. Even when they took mistresses, the Ptolemaic Pharaohs' known concubines were all fellow Greeks (from either Alexandria or Cyrene, a Greek colony which long predated the first Ptolemy & Alexander).

So yeah, it's literally more likely that MLK was part-white than it is that Cleopatra was part-black (sub-Saharan African), or even Egyptian. Frankly, much more likely at that. (The Ptolemies generally had a much more elitist attitude toward their Egyptian subjects than the Seleucids had toward their Persian & other Asiatic subjects, and certainly weren't known for taking Egyptian wives, much less sub-Saharan black ones.)