Lottery officials only know that the ticket was bought in Stevenage and Hitchin, Hertfordshire on June 8. Locals in the town believe that the winner of the jackpot may have died.
Another winner, in Belgium, claimed their prize for the same draw.
Despite the major publicity campaign launched by Camelot in an effort to find the winner before the deadline, no one came forward.
The National Lottery Good Causes scheme will benefit from the winnings.
The winning ticket had five numbers – 5, 11, 22, 34 and 40 – plus Lucky Star numbers 9 and 11.