Adam King and Lucy Rogers after their "peculiar" proposal (Alex Lenati/Evening Standard/Evening Press)

The first night that Lucy Rogers, 26,  met Adam King, 34, both of London, they slept together.

The two met at a friend’s party. When King discovered that Rogers and a friend needed a place to bunk for the night he suggested (innocently, he insists) that they stay at his place.

She and her friend drew straws to determine who would share a bed with King. Rogers drew the short straw.

That was the last they would see each other for three years when they met again at a party.

Rogers recalled that she shouted at King, “I slept with you!”.

“That’s how we started dating,” she said.

“It was a peculiar circumstance,” King admitted.

Six years later, such peculiarities appear to have become happenstance for the pair. On Tuesday,  King proposed to Rogers on a commuter train amidst the mellifluous sounds of his choir singing Bill Withers’ “A Lovely Day”.

King, who owns a tailoring company, knew that the proposal had to top their introduction. In April he began talking with a show choir that he sings with, the Adam Street Singers, to set the singing surprise up.

On Tuesday, the pair was headed to a friend’s house. King had alerted the group of about 25 people that they were to take the train. But Rogers unknowingly almost ruined her own proposal when she suggested that they drive instead. King had to disconnect the car battery to ensure that everything went according to plan. They just narrowly caught the 7:57 train from Euston. As they were seated, one man from the group began singing.

“I’m sure she thought he was loony,” King said.

With a look of pure delight on her face, Rogers watched as more and more people joined in, even soliciting her boyfriend to take out his phone and film the spectacle.

“She  didn’t realize for an instant that it was for her,” King said.

“No part of me was thinking that this might be happening,” Rogers said.

Hoards of people moseyed through the train, stopping at the final refrain as King bent down on one knee and asked Rogers simply, “Will you marry me?”

Crying and shaking, the shocked and elated Rogers said yes.

King said that the over-the-top proposal was just a natural reaction to the way his fiancée makes him feel.

“Something about her, she really rocks my world,” he said.