Tencent’s CEO and chairman, Pony Ma, and founder of ByteDance, Zhang Yiming, were caught bickering today on their WeChat Moments, a function similar to Facebook’s wall.

Tencent is the parent company of WeChat while ByteDance is the parent of Jinri Toutiao and Douyin (called Tik Tok overseas).

Zhang Yiming shared the news that ByteDance’s short video app Douyin became the most downloaded non-game app in Apple’s App Store. The app topped the charts in the first quarter of 2018, according to research by Sensor Tower.

However, Zhang apparently couldn’t help but add a remark directed against the very platform he was sharing the news. In a move rarely seen among tech moguls of any nationality, Zhang accused WeChat of making excuses to block Douyin out of the platform, adding that plagiarizing Douyin with its own short video app Weishi (微视) could not stop its growth.

The accusation likely stems from Tencent’s announcement that messaging service WeChat and social platform QQ will suspend direct playback of short video apps (in Chinese) including Kuaishou, Douyin, Watermelon and Tencent’s own Weishi. Users will have to manually copy links and use the browser watch the video. The decision came after a government clampdown on a number of social media and live streaming sites over undesirable content in April.

But there might be another reason why Zhang Yiming was so keen on taking on Tencent. Along with Kuaishou, Douyin is currently among the frontrunners in China’s short video streaming industry, but new entrant apps from Tencent and Baidu are hoping to challenge their dominance. Earlier this month, news broke that Tencent was spending RMB 3 billion ($478 million) in subsidies to lure influencers to an upgraded version of Weishi.

Tencent’s Pony Ma decided to answer Zhang personally, saying that the statement is defamation to which Zhang responded (our translation):

“The former [blocking Douyin links on WeChat] is not suitable for discussion. The latter [plagiarizing Douyin] has been notarized [i.e. evaluated by legal experts]. I didn’t want to go into a verbal dispute. I just failed to resist complaining and now my PR is criticizing me. I’ll send you the materials.”

“There’s too much you need notarized,” Ma responded sharply.

China’s short-form video is one of the country’s fastest-growing markets. According to iiMediaResearch, China’s short video users passed 240 million in 2017 and is estimated to reach 353 million this year. The popularity of short videos and the development of monetization channels also helped boost market revenues to a staggering RMB 5.73 billion ($913 million) last year.