Hilchos Lashon Hara, chapter 3, section 1

The prohibition of lashon hara applies also to the truth, whether he speaks of the person in secret and is concerned lest it becomes revealed that he spoke of him, in which case he transgresses, “Cursed be he who strikes his fellow in secret,” and whether he even feels that he would relate the lashon hara in front of the person spoken of. This is also forbidden and considered lashon hara. Speaking before him can be an even greater prohibition since besides the prohibition of lashon hara, he is behaving with brazenness and sometimes embarrasses the person to the extent that his face pales.