Rubens Barrichello apologized to his Williams team and Fernando Alonso after his 300th grand prix ended in a crash before the first lap was even over.
Celebrations for the veteran Brazilian's milestone start dominated the build-up to the Spa race, but Barrichello became the event's first retirement when he plowed into Alonso's Ferrari under braking for the Bus Stop as the field encountered the first rain shower of the afternoon.
"Despite my experience, it was very difficult to know how wet the track was on the opening lap, but it was fully wet when I came into Blanchimont," said Barrichello.
"I was closing the door on [Nico] Rosberg and when I touched the brakes, even though it was quite early, it wasn't sufficient to stop the car. The car went straight on into Alonso, for which I'm sorry."
He admitted that the retirement was particularly disappointing given the excitement of his 300th Formula 1 start.
"It's also sad for the team," Barrichello said. "We've had such a positive weekend that a good result would have been a nice conclusion. Despite not having a good outcome in my 300th race, I'm confident we will go well in the 301st."
Nico Hulkenberg also failed to score in the second Williams, finishing only 14th as his race was marred by a throttle-control problem.