Britain's Jenson Button will stand in for Fernando Alonso at next month's Monaco Formula One Grand Prix while the Spaniard competes in the Indianapolis 500 on the same day.
Although the 37-year-old Button retired at the end of last season, he remains under contract with McLaren and is taking Alonso's seat for this single race because the team have allowed the Spaniard to make his IndyCar debut on May 28.
"I'm thrilled to be making a one-off return to Formula 1 racing, and I couldn't think of a better place to make that return," Button said in a team statement on Friday.
"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."
Monaco resident Button will be the most experienced driver on the grid in Monte Carlo as he makes his 306th start - third in the all-time lists behind the retired Rubens Barrichello and Michael Schumacher.
He is also the last driver to win a race for McLaren, in Brazil in 2012, but cannot hope for such success this time with the Honda-powered cars enduring a tough start to the season, with no points from two races.
"I realise we won't have a realistic chance of repeating my 2009 victory but I think we'll have a opportunity to score world championship points," Button said.
McLaren racing director Eric Boullier, who offered Button the one-off return, is "truly delighted" the 2009 world champion will be back in the car for the sixth round of the championship.
"Jenson is a class act. He's a superb driver, fast, smooth and precise, and he won't have lost any of his competitive edge over the past few months.
"He'll do a great job for us, I'm sure of that."
The 35-year-old Alonso's motivation to race in IndyCar's premiere race is part of a wider ambition that also includes the Le Mans 24 Hours endurance race.
Alonso flies to Alabama next week to visit his IndyCar team members and then have a seat fitting done. After the Russian GP on April 30, his schedule will become even more hectic.
"After Russia, I will try to be in Indianapolis for a couple of simulator days and hopefully test the car, but it's not 100 percent sure," Alonso said.
"After that I will go to the Spanish Grand Prix (May 14) and then fly to America on Sunday after the race."
McLaren are back in the Indianapolis 500 for the first time in 38 years with Alonso's entry, a Dallara DW12 chassis run by Andretti Autosport.
"I hope he'll have some great stories to bring back to us from Indianapolis," Boullier said.
"You couldn't get two more different racetracks than Monaco and Indy.
"That's the beauty of our sport.
"It also reflects the technical versatility of McLaren and Honda and it underlines the fact that we're racers, above everything else."
Alonso will retake his Formula One seat after Monaco - at the Canadian GP on June 11 - for the remainder of the season.