If you add AlCl3 to water, why does the pH decrease? You are not adding any hydrogen ions, so why does the pH of the solution decrease? 
Thank you in advance.

EDIT: I will add the context of my asking this question to clarify some details. This is not a homework question. I am preparing for an upcoming examination in Chemistry, and I found this statement in the mark scheme of a practice exam I was doing, and yet I don't understand why it is true.

I have learnt pH as simply being the negative log of the concentration of H+ ions. I fail to see how adding the above salt changes the pH, especially since HCl is a strong acid (hence it completely dissociates in solution). 

Thought process: Is the pH change a result of Aluminium forming Aluminium Oxide?
A more clarified reaction in addition to Berry Holmes' answer:

$$\ce{AlCl3 + 4H2O &lt;=&gt; [Al(OH)4]- + 3Cl- + 4H+}$$

The reason this happens is the Lewis-Acidity of $\ce{Al^3+}$ as well as the higher affinity for $\ce{OH-}$ ions when compared with $\ce{Cl-}$.