National Lottery players are being urged to check and double-check their tickets for the chance to claim this life-enhancing prize.
The search is now on to find the owner of the winning ticket, bought in South Lanarkshire, who matched five numbers and the bonus ball in the lotto draw on Wednesday, June 4.
The winning Lotto numbers on that date were 14, 19, 30, 31, 47, 48 and the bonus ball was 16.
The lucky ticket-holder has until Monday, December 1, 2014 to claim their prize.
If no-one comes forward with the winning ticket before the prize claim deadline, then the prize money, plus all the interest it has generated, will go to help National Lottery-funded projects across the UK.
A National Lottery spokesperson said: "We're eager to find the mystery ticket-holder and unite them with their winnings - this amazing prize could really make a huge difference to somebody's life. We're urging everyone who bought a Lotto ticket in this area to check their old tickets again or look anywhere a missing ticket could be hiding.
"Try checking in the pockets of clothing, in wallets, bags and down the back of the sofa - someone out there could literally be sitting on a fortune! We have the champagne on ice and our fingers crossed that the lucky winner comes forward to claim their win."
To help jog Lotto players' memories about what was happening at the time, sports fans may well remember that Scotland's own Andy Murray was in action on the day of the draw in the quarter finals of the French Open against home favourite, Gael Monfils. After five battling sets, Murray progressed to face the all-conquering Rafael Nadal in the semi-final. Away from sport, locals may have taken a trip into Glasgow to see a performance of Madama Butterfly -Scottish Opera at the Theatre Royal.
Anyone who believes they have the winning ticket for any of the National Lottery draws within the 180-day deadline should call the National Lottery Line on 0845 910 0000.
Anyone concerned about lost or unchecked tickets may like to consider either setting up a National Lottery Subscription or playing online at www.national-lottery.co.uk.
Numbers can be entered in advance and lucky winners are notified online if their numbers come up. For further information call 0845 912 5000 or visit www.national-lottery.co.uk