The Layer Cake actress first sparked pregnancy speculation in August when she was photographed with a baby bump on a beach holiday in Ibiza and she later flaunted her growing stomach on the red carpet at Vogue World in September. On Wednesday, the latest cover for Vogue magazine was released, featuring the 41-year-old bearing her bump on the cover. The accompanying maternity photoshoot, shot by Annie Leibovitz, depicts Sienna with her boyfriend Oli Green, 27, and her 11-year-old daughter Marlowe. During The Run-Through with Vogue video interview, Sienna said of her pregnancy…