With the Monaco Grand Prix already in the bag, Alonso is plainly still deadly serious about becoming only the second driver to have won motorsport's so-called Triple Crown alongside Graham Hill. The active driver closest to matching the achievement is Juan Pablo Montoya, who won the Indy 500 in 2000 and 2015, and won the Monaco grand prix in 2003, although he is yet to race at Le Mans and is unlikely to feature in this year's race either.
The most grueling part of Alonso's schedule will see him driving in either F1 or the WEC on seven consecutive weekends, starting with him competing in the Monaco Grand Prix on May 27 before testing for Le Mans on June 3.
The latter he's ticked off twice, while he came close to glory at Indy 500 in 2017.
Better yet, Alonso will get two shots at Le Mans in a single season thanks to the WEC's one-off decision to extend the next championship into 2019, creating a "super season".
"I am looking forward to seeing how much Toyota Gazoo Racing will grow when our drivers and all team members take what they have learned thus far in endurance racing and add to it what they will gain from Fernando's experience", Toyota president Akio Toyoda said.
"My deal to race in WEC was only made possible through the good understanding and strong relationship I have with McLaren, and I'm very happy that they listened and understood what this means to me".
'In no way will this challenge take away from my main target of Formula 1 with McLaren.
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Alonso and McLaren have high hopes for much-improved F1 results this season following the team's move from Honda to Renault power, and the two-time world champion insists his WEC outings will not be a distraction.
Alonso took part in the Daytona 24 last weekend, finishing 13th alongside team-mates Lando Norris and Phil Hanson.
"It's no secret that Fernando has wanted to contest the Le Mans 24 Hours", Zak Brown, Executive Director, McLaren Technology Group, said in a media release.
"Like Fernando, at McLaren we're racers at heart, and our team is built on a fearless heritage of competing and succeeding in different forms of the sport".
"McLaren and Fernando are in full agreement that Formula 1 remains their shared top priority".
Alonso will miss Toyota's home round at Fuji, due to his required participation at Formula 1's United States Grand Prix, but will compete in each other event. Equally important is the confidence that nothing detracts from our number one goal of Formula 1.
'After proper evaluation, we are satisfied that this campaign does not (compromise that), and that McLaren's best interests prevail'.