Germany is famous for having no speed limits on stretches of its motorways, but a Czech millionaire appearing to do 417km/h (260 mph) may have been testing the limit of what's tolerable.
Radim Passer is now being investigated for his apparent drive along a motorway in the state of Saxony-Anhalt.
The prosecutor's office in Stendal said it had launched a probe into the potentially illegal incident.
The driver faces a prison sentence of up to two years or a fine, reports say.
The wealthy sports car owner from the Czech Republic posted videos of last summer's apparent drive in a Bugatti Chiron on the A2 between Berlin and Hanover on YouTube, bringing attention to the incident.
In the videos, the car's speedometer appears to display a speed of up to 417km/h.
In written comments beneath the video, Mr Passer says: "There was visibility along the whole stretch. Safety was a priority, so the circumstances had to be safe to go." He adds that the drive took place at 04:50 on a Sunday morning and there had been an earlier drive-through of the stretch of motorway.
Police launched an investigation after the alleged breach was reported in German media.
According to the criminal code, a solo drive can still constitute an offence if the driver "moves at an inappropriate speed and in a manner that grossly violates the traffic code and is reckless", reports say.
Transport Minister Volker Wissing has condemned the driver's attitude, noting that while there is no speed limit in Germany, the car should always be "under control", the AFP news agency quotes him as saying.