It started when Merlin walked into his flat after a particularly long and tiring day at work and had a near heart attack when he found his living room full of people yelling "SURPRISE!" at him.

The yelling had tapered off quickly as Merlin raised his fists because really, burglars were not what he needed to deal with. He'd taken in the presents and the gigantic cake that read "Happy Birthday Arthur!" on it, and the people's faces as they realized that they had maybe thrown their party in the wrong flat.

There was some shouting as Merlin demanded to know what the hell was going on, his voice definitely not two octaves higher due to the fright. The group of strangers had explained that their friend, whose birthday it had been a few days ago and who had been recently thrown out of his father's house, could do with some cheering up. Then a man who introduced himself as Gwaine sheepishly confessed that he had been more than a bit drunk the only time he'd visited his friend's new flat, and maybe had gotten the numbers mixed up. Merlin made a mental note to find a new hiding place for his spare key.

As the strangers apologized and started to pack up, and Merlin's heart rate returned to normal, Merlin decided that this Arthur bloke, whoever he was, deserved to be surprised today. Plus, his friends looked so disappointed as they packed up their party, and it wasn't like Merlin had had plans for that night anyway.

So he'd sent one of the strangers, whose name was Lance, to fetch the birthday boy and tell him his neighbor had collapsed and they needed to come to this flat right away to call an ambulance, or something.

So the surprise part of the party still happened, Arthur turning out to be an incredibly hot blonde man who had an adorable when confused, and then the people all packed up the party and prepared to move it to Arthur's room.

After the strange location of the party had been explained, Arthur approached Merlin and apologized for his friends and, after some coaxing, convinced Merlin to come to Arthur's flat for at least one drink for all the trouble his friends had caused him.

Merlin had accepted, because this Arthur really was gorgeous, plus it was his birthday, plus the wine he was being offered was more expensive than anything he'd ever drunk.

So he'd ended up laughing and drinking with Arthur and his friends, who turned out to be great and funny people, and one drink turned into two, which turned into three, and then he lost count.

That was how Merlin found himself sitting on his neighbor's couch snogging the life out of him as his neighbor's friends whooped and catcalled around them.

Merlin supposed it should have been weird, making out with a man who was pretty much a stranger, but it wasn't as though he'd never done this with strangers before. And this stranger's lips were especially nice, particularly when his tongue slipped into Merlin's mouth and Merlin put his hands on Arthur's hips, which he noted were very nice indeed. Then Arthur slipped his leg between Merlin's and Merlin let out a moan, and then Arthur was pulling away to shout at his friends to get the hell out of his flat. Which they did, but not before someone threw a handful of condoms that had "Congrats on the birthday sex!" printed on the wrappers.

Arthur and Merlin kept a close relationship after that, and then one day, six years and six birthdays later, Merlin walked into his flat to another surprise.

Arthur was waiting for him in his living room, which wasn't such a surprise, but then he slid down and landed on one knee, and Merlin was definitely surprised when Arthur pulled out a ring and asked Merlin to marry him.