Now BYD's stock is over HK$42, an increase of about 400 percent. That means Berkshire's original $230 million investment is now worth about $1.2 billion on paper.
Buffett's willingness to back the company has helped boost the stock price, of course. BYD soared 42 percent in the day after it was announced, but at that point it was still below its high of HK$20 from the previous year.
BYD's all-electric e6 automobile made its Detroit debut last January at that city's auto show, and then got major attention in April when a Fortune magazine cover story highlighted Buffett's investment in the "car of the future."
That story also notes that Buffett doesn't get all the credit for this particular billion-dollar profit. The investment was first suggested by his partner, Charlie Munger.