A source told HollywoodLife.com that Taylor didn't make Harry's star-filled guest list because he thought that would be "inviting drama."
The insider revealed: "She was never invited because he wanted to have fun and inviting drama and all the nonsense she would bring is never fun. Why bring oil in a party full of water?"
Um. Okay. Who's having a party full of water? Odd.
The source continued: "She would want to be the center of attention, and it was his birthday. He wants to be the master of ceremonies so to speak, he doesn't want to babysit her and have to watch who she is talking to."
Yeah, we're not exactly sold on this theory either, but the source added, "He didn't want to make his birthday something more than what it was, by adding Taylor it would have added so many elements to the night and he wanted to have fun. Taylor being there would have meant he would have had no fun, simple as that."
We had a feeling some "source" would come forward with a theory about why Tay wasn't there. We're guessing Taylor had plenty going on to keep her busy and, after all, she didn't invite him to her birthday party!