Pascal Wehrlein leapt rapidly from the Force India to the Mercedes cockpit as the Barcelona test began on Thursday morning.
The 20-year-old German had just started running in the 2014 Force India when, in the works Mercedes, reigning world champion Lewis Hamilton fell ill.
“Lewis Hamilton is unwell and not able to continue driving today,” the German giant confirmed.
Wehrlein, Mercedes’ 2015 reserve driver, was on loan to the similarly-powered Force India team for half of the four-day Barcelona test.
He had only completed a few laps before Mercedes confirmed on Twitter that “We’ve borrowed him back from our friends Force India. Thanks guys!” (GMM)