This Christmas will be one a NSW great-grandfather will never forget after he claimed the $1 million division one Lotto prize pool last Monday night.

The man, who wished to remain anonymous, reportedly swore in disbelief when he discovered he had won.

"It would be an understatement to say that I am excited and shocked," he said.

"My late wife chose the winning numbers so they are very special to me.

"I have been playing them since she passed away so I am sure she will be looking down and smiling on me."

The winning ticket was purchased at Cootamundra Newsagency in southern NSW with owner Peter Ruxton over the moon for the winner who has become the store's biggest prize winner.

"We're absolutely thrilled about it," he said.

"Our biggest one was about $500,000 and that happened around 18 months ago."

Despite being stunned by the windfall the man was able to tell staff he would be looking to spend the money on the ones he loves the most.

"At my age this is the perfect time to win because I will be able to use the money to help my family," he said.

"There is no way I could spend $1 million on my own."

NSW Lotteries are encouraging players to register their details, spokeswoman Elissa Lewis said.

"Despite being registered, Monday's Lotto winner hadn't updated his contact details so we were unable to contact him to tell him the exciting news," she said.

"Thankfully he wasted no time in checking his ticket and discovered that he had won $1 million."

Those wishing for another chance to win big will have their chance before New Year with this Saturday's Lotto $30 million Megadraw.