The Daily Mail says it was reported that the partner of De Bruyne became embroiled in an affair with team-mate Courtois.
It is reported by a Belgian gossip magazine that Courtois and De Bruyne's 20-year-old girlfriend exchanged explicit pictures on Facebook.
The magazine reports that Caroline Lijnen became frustrated at life with De Bruyne in Bremen and moved to Madrid where she enjoyed a liaison with Courtois.
De Bruyne was said to be "devastated" upon hearing the news.
A source in the magazine said: "In the Madrid house she cheated on Kevin. He didn't know anything, but when he discovered about it, he went crazy. It was a huge shock for him."
The Belgium team-mates are said to have since rekindled their friendship after holding clear-the-air talks before their country's clash against Macedonia.
And a spokesperson from the Belgium FA claimed they now laugh about it.
"They still get along," said a press officer of the Belgian FA. "They even joke about it."