It has been a tragic month for racing enthusiasts.
Last week, British IndyCar star Dan Wheldon died in a fiery accident.
On Sunday, Marco Simoncelli, one of the best motocross riders in the world, was killed in a horrific crash at the Malaysian MotoGP motorcycle race in Kuala Lumpur.
The 24-year-old Italian crashed after being hit by two other riders, and was then sent to the local medical center where he was pronounced dead 45 minutes later of chest, head and neck injuries.
Simoncelli was motionless on the track following the collision, and his helmet had come off.
How the crash occurred was difficult to tell. Simoncelli had lost control of his Honda at Turn 11, just four minutes into the race, His bike regained partial grip and swerved across the track, where he ended up in the path of Italian racer Valentino Rossi and American Colin Edwards.
Edwards dislocated a shoulder in the crash, but Rossi returned to the pits.
Officials were interested in restarting the race, before they learned the extent of Simoncelli's injury. The race was later cancelled as news became more clear, and as fans threw bottles in anger.
Race director Paul Butler said there will be an investigation into the crash.
Simoncelli won the 250cc world championship in 2008 and clinched the crown in Sepang. He moved up into MotoGP in 2010 where he finished eighth overall last season.
Marco was flamboyant on and off the track, said Matt Roberts, a BBC MotoGP broadcaster. When someone dies, everyone always says they loved life. But he had a very vibrant personality. He already had a huge fanbase around the world, partly down to aggressive riding, but also because he was just a cool guy. He didn't take himself too seriously and would have been a big star for next year.
Newly crowned MotoGP champion Casey Stoner of Australia feared for Simoncelli the moment he witnessed the crash.
As soon as I saw the footage it just makes you sick inside, Stoner said to the BBC. Whenever the helmet comes off, that's not a good sign.
The Italian motorcycling federation canceled all events planned for Sunday at the Mugello circuit near Florence.
Simoncelli's death was the first in MotoGP since Daijiro Katoh died from injuries at the 2003 Japanese Grand Prix.
Sunday's fatal accident comes just seven days after Wheldon crashed and died in Las Vegas. Wheldon's funeral services were held on Saturday.
Here's a look at the accident: