On the gulls' road.: how long before the present day section of the story does the flashback take place?

The flashback happened 20 years after the actual event. 

The narrator was a man. He used the first person point of view. His flashback was prompted by a question about a red chalk drawing that was displayed in his study. He recalled the time when he was on a ship and met a woman he fell in love with.

She was married and a mother. Thus, they union cannot be. She was also very ill because of her heart condition. Her name was Alexandra Ebbling and she was the woman on the red chalk drawing and he drew her.