Spice Girls star Geri Halliwell’s husband, Christian Horner, has been accused of “acting inappropriately” by a female colleague. Horner, 50, who has been the principal of the Red Bull Formula 1 racing team since 2005, is now under investigation, RadarOnline.com has learned. A source within the Red Bull team described the allegations as “incredibly controlling behavior” toward a female colleague, according to the Daily Mail. Evidence to support the allegations remains unknown at this time. Horner “completely” denied the allegations, which he called “nuts.” He is expected to remain employed in h…