Ms Melissa Chan was given the lyrics to a love song played over a few speakers at Changi Airport and, soon, several people were dancing to Happy Together outside the cafe she was in.
Even as customers and staff at Caffe Ritazza whipped out their smartphones, the 26-year-old teacher remained clueless as the flash mob grew around her.
Two singers then walked with her to an area near the check-in counters at Terminal 1's departure hall, where about 100 people - including her fiance John Khoo - sang and danced. Even the airport mascot, Max, joined in.
Ring in hand, Mr Khoo, 29, went on bended knee and popped the question. The crowd cheered as he announced: "She said 'yes'."
The flash mob marriage proposal took place on Dec 11 and a video of the unusual move has drawn much attention online.
The 10-minute video was posted on YouTube on Wednesday, and on citizen journalism website Stomp on New Year's Day. It has since attracted more than 125,000 views on YouTube.
"I've had strangers posting messages on my Facebook page to congratulate me," said Mr Khoo.
The flash mob was organised by Glee Studios Singapore and the Singapore Show Choir Academy. Mr Khoo is the co-founder of both groups.
He told The Straits Times he got the idea after discussions with his students at the academy.
"I thought it'd be fun, and I would also be able to invite my friends and students, who are part of my life," he said.
Proposing at the airport would be a good way to start their holiday, he added. They were going to Bangkok and Taipei.
"She wanted something personal and quiet, but I hoped to make it more memorable for her."