The meaning of "A"

[Surapon Vatanavigkit]

The following paragraph appears in a recent AP report on the meeting in Madrid:

A frustrated King Juan Carlos, seated next to Zapatero, leaned toward Chavez and loudly asked: "Why don't you shut up?" The monarch then left the chamber.

Question: What is the meaing of the indefinite article "A" at the beginning of the paragraph? King Juan Carlos is a well-known personality, shouldn't "The" is a better choice than "A"?

[jaykaylam]

King Juan Carlos may be a well-known personality, Surapon, but the report is introducing a "frustrated" King Juan Carlos for the first time.

Hope this helps.