Things had got a bit weird at the North Pole. Santa had disappeared. The disappearance was not weird but the manner in which it happened was. Mrs Claus had finished decorating the Christmas tree and called Santa in for his opinion. As he walked through the door there was a sound like a thunder clap, a puff of smoke and an explosion of gold glitter. When tje smoke had cleared, where Santa had been stood were two young men dressed in red and white. It wasn't unusual for Santa to regenerate it had happened may times over the years, Santa was after all from the planet Gallifrey. His Time Lord technology and skills came in very hand for delivering millions of presents every Christmas Eve.
After a brief discussion it became evident Mrs Claus would need to make a choice of which man she would re-marry and thus who would become the new Santa. Mrs Claus stood there looking at the two handsom choices she had. "I've made my decision" she announced "how would you two fine young men feel about living as a thruple"? They both agreed that it was a great solution to current predicament. And that is how the North Pole gained its first thruple and the world came to have two Santa's.