Kayleigh Moran, 20, was in town in Ashton-under-Lyne, Greater Manchester, with her one-year-old daughter, Daisy, when a stranger approached and handed her an envelope, telling her not to open it until he had gone.
A bemused Kayleigh assumed that the piece of paper was a note asking for money. But when she opened the envelope, she was astonished to find it contained £200 cash and a card which read 'Happy Christmas'.
Kayleigh says she has no idea who the man was or why he chose her, but the 'Secret Santa' could hardly have known just how much of a difference his gift has made to the mum and daughter's Christmas.
Kayleigh, who works as a waitress, had resigned herself to spending Christmas alone because she could not afford the train fare to see her mum in Porthmadog. But thanks to the surprise Christmas present, she will soon be heading off to Wales for a family celebration.
"I have never missed a Christmas with my mum and it would have been horrible," Kayleigh told the Manchester Evening News, "But this means I can go and see her now."
Kayleigh's mother, Shelley Wilde, admitted that she was 'dreading' Christmas without her daughter and baby granddaughter, but now she 'can't wait'.
"Something like this really restores your faith in people," she said.
The mystery donation meant even more to the family because it enabled them to give Kayleigh's recently deceased grandmother a fitting tribute.
"We couldn't afford a proper grave, just a wooden cross," Kayleigh explained. "But I have bought some ornaments that we're going to go and put on her grave on Christmas Day."
But the mum-of-one decided not to spend all the cash on herself, and instead chose to 'pay it forward' by contributing to the Christmas toy appeal for needy children organised by charities every year.
"I don't think the man would want to be recognised," Kayleigh said. "But it means so much and I just want to say thank you."