The executive says he already had the key design/engineering elements in his mind five years ago.

Elon Musk has reaffirmed Tesla's promise to build an all-electric pickup truck.

"I promise that we will make a pickup truck right after Model Y," he wrote on Twitter, responding to a plea from the Vancouver Seed Bank.

The executive says he already had the key design and engineering elements in mind five years ago, suggesting the idea took a higher mental priority as the Model S began to arrive in showrooms.

The company recently teased a pickup at its semi unveiling event. A sketch shows a massive truck, apparently big enough to fit an F-150 in the bed, however Musk suggests Tesla's pickup will actually be similar in total size.

"Maybe slightly bigger to account for a really gamechanging (I think) feature I'd like to add," he added.