The London Metropolitan Police and officials at Heathrow Airport are investigating a security lapse that somehow allowed a 12-year-old boy to board a British Airways flight without a ticket.

The boy ultimately was identified as an unauthorized passenger after he arrived on the Los Angeles-bound plane and a crew member asked to see his boarding pass to show him to his seat.

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The 12-year-old was not traveling with any parents or guardians. It is believed that he arrived at Heathrow and was meant to change flights at the airport, The Telegraph reported.

“We are working with our police colleagues and British Airways to understand how an unauthorized passenger boarded the incorrect aircraft,” a spokesperson for Heathrow told the outlet. “The individual did not represent a security risk and, purely as a precaution, the aircraft in question was re-screened and has since departed. We apologize for the disruption and will continue working closely with the authorities and our airline partners to keep the airport safe.”

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British Airways apologized to affected passengers, one of whom claimed the flight to Los Angeles was delayed by nearly five hours due to the unauthorized passenger. (iStock)

British Airways, too, apologized to affected passengers, all of whom were deplaned and subjected to a secondary screening following the incident.

“We have apologized to our customers for the delay to their flight after an issue during boarding. The safety and security of our customers and crew is always our top priority and everyone who had boarded the aircraft had been subject to security checks,” the carrier confirmed in a statement obtained by Fox News.

“We conducted additional precautionary screening as soon as this issue came to light and we are assisting the police with their enquiries. “

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A passenger aboard the plane claimed the flight was delayed “nearly five hours” following the discovery of the unauthorized passenger, but thanked British Airways for putting safety first.

The passenger further told the Telegraph that crew members, upon questioning the boy, asked passengers if they could translate Dutch, although a spokesperson for Scotland Yard would not confirm his nationality other than saying he was “not a U.K. national.”

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The London Metropolitan Police, Heathrow Airport officials and British Airways are currently conducting investigations.