Why was MLK's Son Dexter King Absent from Dedication Ceremony on National Mall Sunday?

We watched the dedication ceremony for the statue of civil rights icon Rev. Martin Luther King Jr., Sunday on the National Mall and couldn't get over how struck we were at the absence of Dexter King. His brother, Martin Luther King III and sister Bernice King gave speeches in honor of the day, but we failed to see Dexter King anywhere in the crowd. So, is this a sign that all is still not well  among the siblings? Still more infighting?