The schoolboy, from Newall Green, Wythenshawe, Manchester, passed through several security checkpoints before boarding the Jet2.com flight.
The captain was only alerted to his extra passenger when holidaymakers raised concerns shortly into the two hour journey.
He said he had just been looking for a lavatory and kept searching until he ended up on the plane.
He told The Sun: “I went to the toilet and sat there but I couldn’t get out.
His mother Mary, 29, said she thought her son had been abducted when he slipped away from her in a shop near the airport.
Police phoned her more than four hours after he disappeared to tell her “we have found your son, he’s in Rome”, she said.
An airline spokesman said that because the aircraft was connected to an airbridge a head count was not required. »