Kate Hudson is dressing up as a New York Yankees fan for Halloween! The actress won't host her annual star-studded Halloween bash this year so she can cheer on her baseball player boyfriend, Alex Rodriguez, when he plays in game three of the World Series, scheduled for Oct. 31.

"Kate looks forward to her Halloween party and always tries to outdo herself," a friend of the star, 30, says. "But it wasn't even a question to do it this year. As much as she would love to invite everyone to her house, Alex is much more important."

Calling off the soiree isn't the only evidence that Kate's romance with A-Rod, 34, has become extremely serious. Kate recently donned a custom-made 18k-gold-and-diamond Jack Vartanian No. 13 pendant -- in honor of A-Rod's jersey number. "She loves being in love and is planning on building a serious life with him," says the friend. "He's a priority. Something like the Halloween party isn't."

So for now, Kate's making it clear that her red-hot romance comes first. "All she does is talk about Alex," the friend says. "She even plans her movie schedule around him. She's madly in love."

Photo Credit: Startraks