It was their tradition until he was eight.
Every Christmas Eve, Ygraine would make Arthur a mug of hot cocoa with whipped cream and cinnamon on top, Arthur would drink it while Uther set up the tree and Ygraine untangled the faerie lights, and then the two of them would decorate the tree, taking frequent breaks to dance around the living room to the sound of Uther's favorite holiday record. When the tree was finished, Uther would hand Arthur the star and lift him up so that Arthur could set it atop the tree. Ygraine always took a picture of this moment and Arthur still had the album to prove it hidden in his room.
Once the star was set, Uther would dip Ygraine and kiss her under the mistletoe while Arthur ran around them, his scarf and mittens flapping behind him. Then Ygraine would bundle Arthur up in his warmest jacket and they would head out to the yard to build a snowman. While Ygraine rolled the base, Uther would help Arthur hunt through the snow to find the perfect rocks to make the eyes and buttons. The carrot in Ygraine's pocket would become his nose, and Uther's hat and scarf would finish him off. Arthur always insisted on being the one to put the nose on but Uther always ended up doing it himself while an exhausted Arthur slept cradled against Ygraine's chest. Uther and Ygraine would exchange a fond look over Arthur's small blond head and stand by his bedside, holding each other and watching him sleep.
After a while they would creep into the living room, fill the stocking, and place Arthur's gifts under the tree. They never wrapped them, just put them in decorative bags. They learned their lesson after the first Christmas Arthur was old enough to unwrap his own gifts. Their living room had looked like a tornado hit it, shredded paper and bows strewn everywhere. After that year, they would just reuse the same bags every year. Arthur never seemed to notice, too busy shrieking and rushing to show them both what Santa had brought. Uther would nod approvingly and Ygraine would "ooh" and "ah" at the right intervals, pleasing young Arthur and deeply amusing herself and Uther.
Arthur always fell asleep after lunch and that's when Uther and Ygraine would exchange their gifts. It was always just one gift each. They would light a fire in the grate, watch each other unwrap them, kiss in the light of fire, and wonder how they could have ever been so lucky.
Arthur still wears one of those gifts every day, a silver ring inlaid with gold that Uther had given Ygraine on the last Christmas that they spent together. For the first few years after he found it in a drawer, he wore it on a chain around his neck, tucked into his shirt and out of sight. When he went away to uni, he started wearing it on his left index finger, the way photos told him Ygraine had worn it. Before.
The year after Arthur finishes uni, he goes home with the ring on his finger and a tree tied to the roof of his car, digs out the old stand and the decorations, and puts on Uther's dusty record to break the silence of the house.
He's out in the yard lining up the snowman's buttons when he hears the front door open. He's reaching for Uther's old hat when he hears the backdoor open and he's just finished tying on Uther's old scarf when Uther comes to stand beside him. Arthur looks at Uther and Uther looks at Arthur and Arthur's not at all sure if this is going to change anything between them but it's enough right now because Uther is reaching into his pocket and pulling out a carrot. He hands it to Arthur and he sets it in place carefully.
Everything is silent, save for the music lightly filtering out into the night air and Arthur worries the ring on his finger.
"There's cocoa on the stove."
Arthur startles a bit before turning to really look at this man, almost his father again after too long, and he thinks "maybe we'll be alright."