Tax info---just turned 18 in November. Can my father still claim me?

I turned 18 in November and got married on the 31st of December. However, my divorced parents have always had the agreement that she claimed my sister and my father claimed me. I haven't told him that I'm married yet. My husband and I, were waiting for some better, "happier" times to come, before we told everyone. We are filing jointly. How can I know if he can claim me, without spilling the beans? Am I too old because I'm 18 now?