The Definite Article in the Accusative Case for the masculine noun "Brief"

For example, the sentence "Ich entdecke den Brief unter einem Stapel alter Bücher."

The word "Brief" is a masculine noun in German. In German grammar, "Brief" is "der Brief" in the nominative case. However, when a masculine noun is used in the accusative case, the definite article changes from "der" to "den." Therefore, in the sentence "Ich entdecke den Brief unter einem Stapel alter Bücher," which translates to "I discover the letter under a pile of old books" in English, "den Brief" correctly uses the accusative case for the masculine noun "Brief."