(“Under the rule of complete diversity, if there are residents of the same state on both sides of a lawsuit, the suit cannot be maintained under the diversity jurisdiction even when there is also a nonresident party.”); Fidelity & Deposit Co. of Md. v. City of Sheboygan Falls, 713 F.2d 1261, 1264 (7th Cir. 1983) (citing Strawbridge v. Curtiss, 7 U.S. (3 Cranch) 267 (1806)) (“For a case to be within the diversity jurisdiction of the federal courts, diversity of citizenship must be `complete,’ meaning that no plaintiff may be a citizen of the same state as any defendant.”). The removing defendant, as the proponent of federal subject matter jurisdiction, has the burden of proof as to the existence of such jurisdiction. See Spivey v. Vertrue, Inc., 528 F.3d 982, 986 (7th Cir. 2008); In re Brand Name Prescription Drugs Antitrust Litig., 123 F.3d 599, 607 (7th Cir. 1997); Misiak v. Farmer, Civil No. 10-133-GPM, 2010 WL 685895, at *1 (S.D. Ill. Feb. 23, 2010).