The last official Pharoah of Egypt before Octavian took over control on behalf of the Roman Empire was Ptolemy XIV, also known as Ceasarion. After Cleopatra commited suicide, power transferred to him temporaily. Although he didn't rule long, he was technically the last Pharoah of Egypt. He was later murdered, most likely on the orders of Octavian himself, but there isn't much concreate evidence to support this one way or the other.
Part of the reason there may be some confusion over who the last ruler was is that Cleopatra and her son were co-rulers for a time. But Caesarion did outlive his mother, making him the final one.