Nobody has come forward with the £9.5m jackpot-winning lottery ticket to claim the prize - the largest unclaimed fortune in the draw's history.
The unclaimed fortune has earned £120,000 interest
The winner, who bought the ticket in Doncaster, had already lost £120,000 in interest since the numbers 3, 12, 17, 36, 44 and 49 came up on 6 July.
The 180-day limit for claiming the prize expired at 1730 GMT on Monday.
So the £9,476,995 jackpot will now be distributed through the Lotto's Good Causes fund.
A National Lottery official said: "Unfortunately, I can confirm that the ticket-holder did not come forward within the deadline to claim their prize and has now sadly missed out on this substantial amount of money.
"To avoid this situation happening again, we would urge all National Lottery players to check their tickets on a regular basis."
The organiser of the National Lottery, Camelot, had made numerous appeals for people to check their tickets in the hope that the winner may be found.
Over the last 11 years there have been 23 tickets worth more than £1m that have gone unclaimed - the £9.5m ticket became the 24th.
A Camelot spokeswoman said: "Meanwhile, 1,800 millionaires have come forward to claim their prizes."