Nvidia CEO Jensen Huang and SoftBank’s Masayoshi Son recently shared a few laughs and some bittersweet memories at the AI Summit in Tokyo. At the center of their banter? SoftBank’s former role as Nvidia’s largest shareholder – and how they decided to let that golden opportunity slip away.

Nvidia CEO Jensen Huang said he turned down a chance to buy out the chip giant, while SoftBank CEO Masayoshi Son regretted selling the stock early.

Huang was speaking at Nvidia’s AI Summit in Tokyo where he also announced several AI collaborations with Softbank.

CEO Jensen Huang said at an event in Tokyo that Japanese investment giant SoftBank was once the largest shareholder of Nvidia Corp. Both companies now plan to collaborate in the AI industry.