In what role did the Prince of Wales later serve after laying the cornerstone?

The Prince of Wales later served as King. This connection is significant because the title "Prince of Wales" is traditionally given to the heir apparent of the British throne. Once the current monarch passes away or abdicates, the Prince of Wales ascends to the throne and becomes King. Thus, the actions taken by the individual in their role as Prince of Wales, including laying the cornerstone of an important structure or event, often symbolize their future responsibilities as king.

While the other positions listed, such as Prime Minister, Governor General, and Duke, are notable titles, they do not align with the historical expectations and succession rights associated with the title of Prince of Wales. The correct answer reflects the progression from heir to actual monarch, which is a fundamental aspect of British royal lineage.