Jenson Button will return to F1 to race in the Monaco GP as Fernando Alonso's stand-in, McLaren-Honda have confirmed.
Alonso's unexpected move to compete in next month's Indianapolis 500 has presented McLaren with the opportunity to draft Button back in for F1's showpiece race, just five months after he started a sabbatical.
The two-year deal Button signed with McLaren last autumn allowed him to take 2017 off from F1 competition, but included the proviso that he could be drafted back in as cover if one of the team's race drivers was absent.
"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 than my adopted home Grand Prix: Monaco," Button said.
"I'm looking forward to pitting myself against the unique racing challenge that is the Monaco Grand Prix. I'll drive the MCL32 around Monaco in the McLaren sim beforehand, and I reckon I'll be ready for the race after doing that.
"I'm supremely fit, having done a lot of triathlon training recently, so I have no worries on that score. And it'll be nice to say 'hi' to all my old Formula 1 mates too, and hopefully to give the fans something to cheer about."
Button's contract includes the option of a full-time race return in 2018.
Button, who turned 37 in January, has raced in 15 Monaco GPs, winning the 2009 event for Brawn. He is now set to rack up his 306th F1 start on May 28 - matching Michael Schumacher for second place in the all-time appearance table.
Mclaren's racing director Eric Boullier said: "I was truly delighted when Jenson accepted our suggestion that he race at Monaco instead of Fernando.
"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.
"After all, he's missed only a handful of Grands Prix since his last outing in Abu Dhabi in late November last year, and he's as fit as a fiddle. Also, he's always been good at Monaco. He'll do a great job for us, I'm sure of that."
Button has scored points on each of his last four Monaco appearances, with the low-speed, twisty track again likely to offer McLaren's best early-season chance of a stronger result amid their latest difficult start to the season with Honda.
The Briton has spent recent months in California competing in triathlons and earlier this month came first in his age group at the Ironman 70.3 event, only to be disqualified for cycling too fast through a reduced-speed zone.