McLaren have confirmed that it was a tear-off strip from Fernando Alonso's visor that caused his brake issues in Spain and ultimately his retirement.
The double World Champion was forced to retire from his home grand prix after losing his brakes and overshooting his pit box.
It later emerged that a tear-off strip from his visor had become stuck in his MP4-30's right-rear brake duct and that this led to the failure.
Racing Director Boullier has confirmed the reports.
"It was a tear-off, and we have video footage that shows this," he told Autosport.
"It went straight into the brake duct, obstructing the airflow, so there was no more cooling and that was why, in two laps, the temperatures went through the roof.
"The brake fluid boiled and we lost the brakes, so it was a complete fluke the tear-off should get lodged in there."
This is not the first time in recent years that a tear-off strip has created such drama as Boullier recalled a similar issue hampering Kimi Raikkonen while he was at Lotus in 2013.
"To be honest, I remember the same stupid thing happened with Kimi, that a tear-off went into the front brake.
"Obviously the drivers need them, but we need to maybe think about how and where we throw them. Maybe we need to think about something for the future."