John Cena made one kid's fantasy into a real-life storybook ending -- showing up to meet a boy who was told his family was fleeing Ukraine ... just to meet the wrestling superstar.
WWE released this video earlier in the week, showing JC pop up in Europe to meet Misha Rohozhyn -- a teenager with Down Syndrome, who was forced to escape his native city of Mariupol in recent months because of the Russian attack.
The story goes ... Misha, who's non-verbal, was confused and distressed about leaving home -- as he didn't quite understand what was happening.