Serena Williams is claiming her status as the greatest of all time.On Saturday, the 23-time Grand Slam champion stepped out in a black sweatshirt emblazoned with the acronym 'G.O.A.T.' as she enjoyed Milan Fashion Week with her husband Alexis Ohanian Sr. and four-year-old daughter Olympia.The tennis pro's sweatshirt was from her own fashion line S by Serena and the lettering featured black and white images of Serena on the court.