Every so often, the idea is floated that it would be great for Formula 1 to welcome guest drivers for one-off appearances.
That is never going to happen in an actual Grand Prix and so the sight of NASCAR or IndyCar greats going up against Lewis Hamilton or Max Verstappen is just a dream - but in NASCAR, it is happening.
At this weekend's Cup race at the Circuit of the Americas - home of the United States Grand Prix - on the entry list are two F1 World Champions: Jenson Button and Kimi Raikkonen.
It is Button's NASCAR Cup debut while it is a second race for Raikkonen after his debut at Watkins Glen in 2022.
Here is RacingNews365's guide to everything you need to know about both NASCAR and ahead of the race on Sunday evening.
How does NASCAR work?
You'll be forgiven if you are something of a NASCAR novice, stock car racing's highest level is something of an acquired taste.
Essentially, NASCAR is a spec series with every car coming from one of three manufacturers, with a bunch of parts the same in every car on the grid.
Drivers will race a Ford Mustang, Chevrolet Camaro or Toyota Camry depending on which manufacturer their team has partnered with.
In this case, Button is in a Mustang and Raikkonen in a Camaro.
The race is set to be a 68 lap affair, run similar to the F1 Grand Prix. There will be a rolling start up the hill to Turn 1.
NASCAR has done away with its stage format for the road courses in 2023 so the race will run until any caution periods, like a Safety Car in F1.
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Can Button or Raikkonen win the race?
It is unlikely that either Button or Raikkonen will be the winner come Sunday afternoon, but of the two, it is 2007 champion Raikkonen who has the better chance.
Button is racing for the tiny Rick Ware Racing team in the #15 car. RWR has a technical alliance with Roush Fenway Keselowski Racing - the team of 2012 Cup champion Brad Keselowski.
However, results are difficult to come by the team and so a finish and Top 20 result would be standout from Button.
As for Raikkonen, he is once again driving the #91 Trackhouse Racing entry.
Trackhouse won at COTA in 2022 with Ross Chastain - he of riding the wall at Martinsville infamy - and on another road course at Sonoma with Daniel Suarez.
During his debut at Watkins Glen last year, Raikkonen climbed into the top 10 and was on for a good result before being caught up in someone else's accident and pushed into the wall.
The Finn also took his last Grand Prix victory at COTA, for Ferrari in the 2018 US GP.
Is anyone else guest racing at COTA?
There are some big names on the entry list for the race, with Jordan Taylor and Jimmie Johnson both set to take the green.
IMSA champion Taylor is driving the #9 Hendrick Motorsports Chevrolet - in place of 2020 champion Chase Elliott.
Elliott is out for the foreseeable future after breaking his leg in a snowboard accident. Elliott is arguably the best road course racer in NASCAR, and won the inaugural COTA race in 2021 in torrentially wet conditions.
He will be a guest announcer for Fox.
It might seem weird calling seven-time champion Jimmie Johnson a guest driver, but he is only doing a part-time schedule on his return to NASCAR.
Johnson left Cup in 2020 to go IndyCar racing, but has now retired from full-time competition, instead taking part in select races for his own Cup team, Legacy Motor Club, driving the #84 machine.
Elsewhere, IndyCar star Conor Daly is set to race with The Money Team, owned by boxing legend Floyd Mayweather.
Who are the main contenders?
Some of the older generation of NASCAR drivers such as Kevin Harvick, Martin Truex Jr and Keselowski are not what you'd call road course racers, although Harvick does have a fair record.
Instead, the next generation of Cup drivers have tended to stand out during recent races.
The last road course event in October 2022 was held on the Charlotte roval, and won by Christopher Bell of Joe Gibbs Racing.
Other major contenders will be 2021 champion Kyle Larson at Hendrick Motorsports, who won at Watkins Glen last term, and Tyler Reddick.
Reddick races the #45 23XI Racing entry for the team owned by NBA icon Michael Jordan, having switched across from Richard Childress Racing.
Reddick claimed three wins in 2022, two of those coming on road courses, at Road America and on the Indy road course.
Also a strong road course ringer is AJ Allmendinger.
He is once again tackling a full season with the Kaulig Racing squad - taking victory at Indy in 2021 in the Chevrolet.
Allmendinger was a contender at COTA in 2022, but was shafted out of the way on the last lap by winner Chastain.
Anything else I need to know?
If you're a fan of track limits, let's just say they are not in the vocal of a NASCAR driver.
Drivers will run wide at every corner possible, with the exception being the esses in sector 1 where they are not allowed to have all four wheels off the race track.
Everywhere else is fair game.
Haas F1 boss Guenther Steiner will be the Fox commentary booth, alongside lead commentator Mike Joy.
Joy is joined by full-time Fox analysis Clint Bowyer (in the Martin Brundle role), 2004 champion Kurt Busch, Steiner and Elliott.
If Chastain wins, he will throw a watermelon off the car in celebration of his roots as a watermelon farmer in his native Florida.
The green flag is set for 15:49pm ET on Sunday afternoon, which is 20:49pm ET in the UK.
The race will be broadcast in the US on Fox and in the UK on Viaplay - and remember those clocks go forward...
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