McLaren have confirmed that Jenson Button will replace Fernando Alonso at the Monaco Grand Prix next month.
Button took a sabbatical from Formula One this season, but the 2009 world champion agreed to stand in if a reserve driver was needed.
The Brit has now been called upon after Alonso was allowed to race in the Indianapolis 500 on May 28 - the day of the glamorous race in the principality.
Two-time world champion Alonso was disgruntled with the Woking-based team's inability to come up with a competitive car even before the season started.
McLaren endured engine problems in pre-season and Alonso has failed to finish the first two races of the year.
Alonso said he would not quit during the campaign, but was given the green light to get behind the wheel for the Honda-powered Andretti team in the United States, as he has an ambition of completing the 'triple crown' - winning the Monaco Grand Prix, Indy 500 and the Le Mans 24 Hours.
Button is relishing the opportunity to race in Monte Carlo, where he will step in to be Stoffel Vandoorne's team-mate, and believes he can finish in the points.
"I'm thrilled to be making a one-off return to Formula One racing, and I couldn't think of a better place to make that return than my adopted home grand prix: Monaco." he said.
"I've won the race before, in 2009, and it's one of my all-time favourite racetracks. It's a tricky street circuit on which a good driver can really make a difference – and, although the McLaren-Honda MCL32 hasn't begun the season well, I think it may be more suited to Monaco than to the faster circuits that Fernando and Stoffel have raced it on so far this season.
"Okay, I realise we won't have a realistic chance of repeating my 2009 victory, but I think we'll have an opportunity to score world championship points, which will be very valuable to the team in terms of constructors' rankings."