Translations for confidential in French

Here are paragraphs from public domain books translated:

And he pinched me again, in the most confidential manner.	Et il me pinça derechef, de l’air le plus confidentiel.
Treasure Island, by Robert Louis Stevenson	L’Île au trésor, de Robert Louis Stevenson

A man was introduced of simple mien, who had the appearance of a tradesman. Planchet, by way of dessert, would have liked to hear the conversation; but the citizen declared to d'Artagnan that what he had to say being important and confidential, he desired to be left alone with him.	Un homme fut introduit, de mine assez simple et qui avait l’air d’un bourgeois. Planchet, pour son dessert, eût bien voulu entendre la conversation ; mais le bourgeois déclara à d’Artagnan que ce qu’il avait à lui dire étant important et confidentiel, il désirait demeurer en tête à tête avec lui.
The Three Musketeers, by Alexandre Dumas	Les Trois Mousquetaires, de Alexandre Dumas