Updated

Chinese Olympic swimming champion Sun Yang has apologized for driving without a license after a bus rear-ended the Porsche SUV he was driving.

The four-time Olympic medalist said that as he was usually busy with training and competing he had weak knowledge of the law, which had led to the mistake.

Sun told his 20 million followers on his microblog Monday that he had been driving his relative's SUV when it was rear-ended by a bus on Sunday afternoon in the eastern city of Hangzhou.

He admitted he didn't have a driver's license and said the traffic police were still investigating the incident.

Calls to Hangzhou police rang unanswered. The official Xinhua News Agency reported that Sun faces a fine up to 2,000 yuan ($325) and a maximum 15-day detention.