Anna couldn’t believe it when she saw Duke alive and well in Port Charles in 2012 and thought they could go on with their lives where they left off years ago. However, the man who looked like Duke turned out to be Cesar Faison in the mask (via TV User Manual).
Anna was crushed, but then in an odd situation, it turned out that Duke was actually alive and had faked his death and joined the witness protection program. Duke was even there for her as she tracked down the kidnapped Robin. However, Duke never seemed to learn from the past and started working for the crowd again, according to Deep soap. This time, he works for Sonny Corinthos (Maurice Benard).
That’s when things went awry again and Carlos Rivera killed Duke in a mob attack shortly after Anna agreed to run away with him and leave Port Charles for good. Anna was so upset that she went against her own code of ethics and shoot Carlos in cold blood.
https://www.thelist.com/754149/general-hospital-relationship-timeline-anna-and-duke/ Relationship time at the general hospital: Anna and Duke