One of Kelly's close friends -- who recently spoke to the actress in France -- tells TMZ, the "Gossip Girl" star was shocked when she saw photos of her arrival at the airport in Nice this weekend surfacing on the Internet, and believes her ex is to blame for leaking her location.

The friend says Kelly believes ... if her ex Daniel Giersch really did set up the shot -- it would be a violation of a court order against exposing the couple's kids to the media.

In the photos, Kelly looks happy -- hugging her kids while they wave a sign reading "Welcome Super Mama" -- but now, she's super pissed.

As you know, Kelly and her ex are embroiled in a bitter custody war. A judge recently named Giersch the "residential parent," meaning the kids have to live in France because he's banished from the U.S. Kelly still lives in the States, and has to fly to France to see her kids for her half of the custody share.