D.
From Freepedia
D. (usually preceded in English by the) is the abbreviation for the Spanish honorific Don and the Portuguese honorific Dom, a mark of high esteem for a distinguished Christian hidalgo or nobleman. It is still the usual form to refer to a known priest, as in French Dom. The use is roughly comparable to the style The Honourable in British custom, but closer to Lord or Lady, although the analogy is a loose one, at best. The female version is Dª for Doña (Spanish) and Dona (Portuguese).
Don/Dom or Doña/Dona is attached to the Christian name, and the person is then addressed as such. For example, if Señor Diego de la Vega is to be addressed as a don, then the correct form of address would not be *"Don de la Vega", but "Don Diego".
In Catalan, the equivalent form is en/na.
