http://i.imgur.com/DeohpD8.png

How can I determine the number of possible pairs of diastereomers here?

Here was the question: "How many pairs of diastereomers are possible in the following molecule? PhCH(Cl)CH(Ph)CH(Cl)Ph" I drew the compound.

For the central carbon with no Cl attached to it, is the a chirality center there? There are two identical branches attached to it, however those two branches can change R/S. So, is it a chirality center?