The Style hitmaker was served with papers from bosses at Orange County, California clothing company Blue Sphere Inc. last year (14) for allegedly infringing on several of their 'Lucky 13' trademarks by using them on her own merchandise.

In July (15), Blue Sphere Inc. executives filed a motion asking a judge to force the pop star to sit through a binding interview, believing she is hands-on with her business and in charge of dealing with trademarks, and on Wednesday (05Aug15), a judge sided with the plaintiffs and ruled Swift must now testify under oath.

Swift's lawyers were hoping to limit the scope of questioning from the prosecution, but their request was denied.

The number 13 has long been a special number for Swift, who previously told MTV News, "The significance of the number 13 on my hand... I paint this on my hand before every show because 13 is my lucky number.

"I was born on the 13th. I turned 13 on Friday the 13th. My first album went gold in 13 weeks. My first number one song had a 13-second intro. Every time I've won an award I've been seated in either the 13th seat, the 13th row, the 13th section or row M, which is the 13th letter (of the alphabet). Basically, whenever a 13 comes up in my life, it's a good thing."

The trademark infringement case is set to head to trial in November (15).