A mystery British lottery player has lost out on a STG64 million ($A99.14 million) fortune after the deadline to claim the prize expired.
The unlucky individual, who bought the winning EuroMillions ticket in Hertfordshire, had until 11pm on Wednesday to collect the massive windfall.
But despite a National Lottery publicity campaign, the would-be multimillionaire missed the 180-day deadline - making the STG63,837,543.60 prize the biggest unclaimed lottery win in history.
The bumper haul of money, plus all the interest it has generated, will now go to the National Lottery Good Causes - adding to the STG29 billion already raised through sales of lottery tickets since the UK National Lottery launched in November 1994.
A National Lottery spokeswoman said: "Unfortunately, I can confirm that the ticketholder did not come forward within the deadline to claim their prize and has now sadly missed out on this staggering amount of money.
"The vast majority of prizes are claimed within the 180 days but to avoid this unfortunate situation happening again, we would urge all National Lottery players to check their tickets on a regular basis."
The now-expired ticket was purchased in the Stevenage and Hitchin area for the EuroMillions draw on Friday, June 8.
National Lottery officials launched a desperate search for the holder, raising awareness through adverts and posters.
The missing ticket-holder matched all five numbers - 5, 11, 22, 34 and 40 - and both Lucky Star numbers - 9 and 11.
Before Wednesday night, the biggest unclaimed lottery win was STG9.4 million after the owner of a winning ticket bought in Doncaster in July 2005 failed to come forward.