Red Bull boss Christian Horner was so taken aback by Daniel Ricciardo's call to tell him that he was moving to Renault that he thought that the Australian was making a joke, according to reports from the British publication The Daily Mail.
Ricciardo stunned the racing world on Friday by confirming a move to Renault on a two-year deal commencing in the 2019 season, after months of speculation regarding where he would race next season.
It is understood that the Aussie had grown tired of a future playing second fiddle to Max Verstappen, but it appeared that all conceivable options had dried up and he was set to stay.
Indeed the report suggests that Horner believed a one-year extension, as per Ricciardo's request, had been agreed, and that the announcement would be made during this summer break.
However, Renault's 11th-hour offer, thought to be worth £20m per season, persuaded Ricciardo to leave and when Horner received the call he thought initially that it was a prank - a video confirming his stay at Red Bull had already been made and was ready for publish.