A 28-year-old male presents to the emergency department following a fall on his outstretched left hand while playing cricket. He reports severe pain in the proximal forearm and inability to pronate/supinate the forearm. On examination, there is swelling over the proximal third of the ulna with a palpable deformity. X-ray of the left forearm shows a fracture of the proximal third of the ulna with anterior angulation, and the radial head appears dislocated anteriorly on the lateral view. What is the most likely diagnosis?