An explosion near the Ognyanovo Reservoir in Bulgaria last October (11) killed stuntman Kun Liu and left fellow action man Nuo Sun - Lundgren's body double - wounded.
Sun, who was hit in the eye by a piece of iron, was hospitalised for several days in Germany, but his condition was later upgraded from critical to stable - to the relief of the cast and crew, who decided to keep filming in honour of Liu's work.
Sun eventually made a full recovery and returned to the set, but Lundgren reveals he struggled to overcome the near-death experience in the weeks that followed.
The Rocky IV star tells the Associated Press, "I could see, like, post-traumatic stress for a month after. Because he was very close to dying. It made us all realise that yeah, it is a dangerous business. You have to watch your steps."
Liu's parents are now suing the film's producers, who have dedicated the movie to the tragic stuntman, for more than $25 million (£15.6 million), claiming executives failed to take proper safety precautions on the set.