Question: The Volkswagen Concept D was envisioned by the chairman of the supervisory board until what date?
Sentence (from "Ferdinand Piëch"): Ferdinand Karl Piëch (born 17 April 1937) is an Austrian business magnate, engineer and executive who was the chairman of the supervisory board ("Aufsichtsratsvorsitzender") of Volkswagen Group until 25 April 2015.
Relevant evidence: Yes