Photographer Craig Shimala was filming a time-lapse of a derecho over Chicago on the night of June 30th when a triple lightning strike touched down on three of the city's tallest buildings: Willis Tower, Trump Tower, and the John Hancock Building.
The whole time-lapse is worth a watch, but the triple strike can be seen at 0:36 and 0:46. Here's the still from the 36-second mark:
"This time [the photograph] was a still from a time-lapse," writes Shimala. (The still, from the 26-second mark, appears above.) He specifies "this time," because he captured another triple-strike – on the same trio of buildings – four years ago: