Breakdown of Wir sehen den Designer, einen sehr bekannten Mann.
ein
a, an (eine)
der Mann
the man
sehr
very
wir
we
Questions & Answers about Wir sehen den Designer, einen sehr bekannten Mann.
Why is it einen sehr bekannten Mann and not ein sehr bekannter Mann?
This is a noun apposition—a descriptive phrase placed right next to a noun to give more information about it. In German, an apposition must always match the case of the noun it describes. Since den Designer is the direct object in the accusative case, the apposition must also be accusative, giving us einen instead of the nominative ein.
Why does the adjective bekannten have an -en ending here?
Because the phrase is masculine (der Mann) and in the accusative case, the adjective follows the indefinite article einen. In this setup, the adjective takes the -en ending. A handy rule of thumb: whenever you have a masculine noun in the accusative, both the article and the adjective will end in -en (einen bekannten).
Do I always need a comma before a descriptive phrase like this?
Yes. In English, we sometimes drop commas around short descriptive phrases, but German punctuation is stricter. Appositions must always be set off by commas. Since this one is at the end of the sentence, it just needs one comma before it. If the sentence continued, you would need a second comma right after Mann.
Could I move the phrase einen sehr bekannten Mann to a different part of the sentence?
No, an apposition is strictly tied to its "anchor" noun and must sit directly next to the noun it describes. If you moved it away from den Designer, the grammatical link would break and the sentence would sound completely wrong to a native speaker.