Fortunately, The Chicago Manual of Style (16th edition) deals with this question on page 388:
8.5 Names with particles. Many names include particles such as de, d', de la, von, van, and ten. Practice with regard to capitalization and spacing the particles varies widely, and confirmation should be sought in a biographical dictionary or other authoritative source. When the surname is used alone, the particle is usually retained, capitalized or lowercased and spaced as in the full name (though always capitalized when beginning a sentence). [emphasis added]
So, following Chicago, the correct sentence is, "De Bernezan entered the room."
The variation in capitalization you found on the De Vries Wikipedia page is explained by the Chicago rule for Dutch names used in an English context (page 390):
8.10 Dutch names. In English usage, the particles van, van den, ter, and the like are lowercased when full names are given but usually capitalized when only the last name is used.
Johannes van Keulen; Van Keulen
Pieter van den Keere; Van den Keere
Vincent van Gogh; Van Gogh
Gerard ter Borch; Ter Borch
