The Spaniard's participation in the Indianapolis event was confirmed in a statement on McLaren's official website.
BBC Sport's Andrew Benson relayed news that Alonso will miss the Monaco race on social media:
According to a report from Benson, the two-time world champion has the "full approval and support of McLaren and engine partner Honda" to make the change. The Andretti team are powered by Honda and will feature McLaren branding.
Within the statement, the 35-year-old Alonso spoke of his excitement at being able to compete in one of the world's most famous races.
"I've won the Monaco Grand Prix twice, and it's one of my ambitions to win the Triple Crown [the Monaco Grand Prix, the Indianapolis 500 and the Le Mans 24 Hours], which has been achieved by only one driver in the history of motorsport: Graham Hill," he said. "It's a tough challenge, but I'm up for it."
Alonso went on to state he wasn't sure when he was going to compete at Le Mans but said he has "plenty of time for that."
As noted in their bulletin, McLaren will be back at the iconic Indy 500 event for the first time in 38 years, entering a single car in the 101st edition of the race.
The Indy 500 does clash with the Monaco Grand Prix, though,—the flagship race on the Formula One calendar—meaning Alonso will not be in situ in Monte Carlo.
"In due course McLaren-Honda will announce the identity of the driver who will race Fernando's car at Monaco," read the statement, although according to Benson's piece, former McLaren man Jenson Button could make a one-off return to the cockpit after his recent retirement.
As noted by BT Sport's Jake Humphrey, the decision made by Alonso not to take part at Monaco might be due to a difficult start to 2017 for McLaren:
After plenty of struggles during pre-season testing, Alonso has failed to get his McLaren over the line in either two of the opening races in 2017, pulling out of the Australian and Chinese Grand Prixs.
Despite the reliability issues endured by the team, Alonso remains one of the most esteemed and experienced drivers on the grid. It'll be fascinating to see how versatile he is behind the wheel when he begins this latest venture.
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