You are seeing a 40-year-old male in A&E who has presented with abdominal pain. The patient informs you during the history that this pain came on suddenly, is located in the epigastric region and is continuous in nature. The pain radiates to the back and worsens with movement. On examination you note abdominal tenderness in the epigastric region, rebound tenderness and guarding. There is also a bluish discoloration around the umbilicus. What is the most likely diagnosis?