Tennis fans ran to social media for answers Monday when TV cameras appeared to show the shadow of a plane flying in reverse at Roland Garros.

Watch for yourself:

The weird occurrence happened during the French Open match between Serena Williams and Sloane Stephens.

Fortunately, there's an explanation. 

There's a camera high above the stadium. As a marketing tool, there is an Emirates Airlines model plane attached to it. 

So when the camera swings back and forth and the sun is in the right spot, fans get to see the illusion of a plane flying in reverse.

You can see the photo of the contraption, here