Marc Marquez completed his first Moto2 laps since last October's Malaysian Grand Prix accident, during a surprise appearance at Alcarras in Spain.
The 2011 world championship runner-up's attendance was not officially announced, but some BSB riders also testing reported the news.
“Pretty cool for Marc Marquez to turn up at Alcarras on his Suter Moto2 bike!” read a Tweet by WFR Honda rider James Westmoreland (@Westybsb27).
A picture of Marquez riding down the pit lane on an unbranded motorcycle with orange wheels also appeared on Twitter.
This [Tuesday] evening, Twitter messages from Repsol (@Box_Repsol) finally confirmed it had indeed been Marquez:
"Hello! Today we have good news to give you: Marc Marquez rode at a good pace at Alcarras and will now train at Albacete.
"Earlier today he did a bit of supermoto, and then completed a total of 8 laps of Moto2. :)"
A later press release then added further details:
"Marc Márquez will be on track in a private test in Albacete this Thursday and Friday. The Repsol rider will head to Albacete tomorrow, having confirmed his positive recovery from eye surgery with time on his Suter Moto2 today. The Spaniard has already received the all clear from doctors following a final check-up this week and many miles onboard a motocross and supermotard bike.
"Márquez was back on two wheels today at the Alcarrás Cirucit. After an early morning Supermotard session he undertook 8 laps onboard his Moto2 bike —in order to make sure that he was ready for a return to testing. The objective in Albacete will be to further evaluate his recovery."
The Repsol Suter star, who won seven races during his rookie campaign, had not ridden a Moto2 machine since suffering eye problems following a practice fall on an unmarked section of wet track at the penultimate 2011 round.
Marquez subsequently underwent surgery to cure double vision problems and, although he has been training on a motocross bike, has missed two of the three 2012 pre-season Moto2 tests.
The final official Moto2 pre-season test will be held at Jerez from March 19-21, with the season-opening race in Qatar on April 8.
19-year-old Marquez, a former 125cc world champion, had previously stated there was a 'small chance' he could miss the opening round, but also that his team was planning private test sessions to make up for any lost time.