  We present a long term optical $R$ band light curve analysis of the
gravitationally lensed blazar AO 0235+164 in the time span 1982 - 2019. Several
methods of analysis lead to the result that there is a periodicity of ~8.13
years present in these data. In addition, each of these five major flares are
apparently double-peaked, with the secondary peak following the primary one by
~2 years. Along with the well known system, OJ 287, our finding constitutes one
of the most secure cases of long term quasi-periodic optical behaviour in a
blazar ever found. A binary supermassive black hole system appears to provide a
good explanation for these results.
