code for filtering twice on combobox

I would like to filter a combobox on 2 basis the first is that I filter combobox3 based on combobox1 selection (I have done this already). The second is that dependent on combobox2 selection, combobox3 is further filtered. I am trying to figure out the code I need for combobox2.

I would like combobox2 to look at the data in combobox1 and then filter the results into combobox3. My scenario is this:

Combobox1 contains authors, if J.K.Rowling is selected combobox3 lists all of her books. If then in combobox2 I select pre 2000, combobox3 would then only list all of J.K.Rowlings books pre 2000 and filter out any post 2000.

Is this possible?

Thanks

Z