SUMMARY ORDER

Simon Property Group, L.P. (“Appellant”) appeals from a judgment of the United States District Court for the Southern District of New York (Robinson, /.), which granted summary judgment in favor of Appellees, Burns International Security Services Corporation (“Burns”) and Lumbermen’s Mutual Casualty Company (“Lumbermen’s”). We assume the parties’ familiarity with the underlying facts, the procedural history, and the issues presented for review.

We review a grant of summary judgment de novo. McBride v. BIC Consumer Prods. Mfg. Co., 583 F.3d 92, 96 (2d Cir. 2009). “Summary judgment is appropriate where there exists no genuine issue of material fact and, based on the undisputed facts, the moving party is entitled to judgment as a matter of law.” Fed. Ins. Co. v. Am. Home Assurance Co., 639 F.3d 557, 566 (2d Cir. 2011) (internal quotation marks omitted); see also Fed.R.Civ.P. 56(a). We also review de novo whether a contract is ambiguous under New York law. Bank of N.Y. v. First Millennium, Inc., 607 F.3d 905, 914 (2d Cir. 2010).

Here, we find no error in the district court’s grant of summary judgment for Appellee Burns. The security agreement between Burns and Appellant stipulates that the parties must initiate proceedings within twelve months of “the date of the occurrence giving rise to such Claim.” The agreement imposes an indemnification obligation on Burns only in case of Burns’s negligence and without *18 regard to whether suit was filed against Appellant. In this context, the operative phrase was sufficiently clear to read the limitations period as running from the incident involving Burns’s alleged negligence-here, the assault. Appellant failed to initiate any proceedings against Burns until three years after this occurrence; therefore, Appellant was contractually barred from bringing the instant claim against Burns.

Likewise, we find no error in the district court’s grant of summary judgment for Appellee Lumbermen’s. Under New York law, “compliance with a policy’s notification provisions is a condition precedent to the insurer’s liability under the policy.” Webster ex rel. Webster v. Mount Vernon Fire Ins. Co., 868 F.3d 209, 214 (2d Cir. 2004). Without a valid excuse, “an insured’s failure to provide timely notice of a claim to its excess insurer is a complete defense to coverage, regardless of whether the carrier was prejudiced by the late notice.” Green Door Realty Corp. v. TIG Ins. Co., 329 F.3d 282, 287 (2d Cir. 2003) (citing Am. Home Assurance Co. v. Int’l Ins. Co., 90 N.Y.2d 433, 661 N.Y.S.2d 584, 684 N.E.2d 14, 16 (1997)).

The insured bears the burden of proving reasonableness of delayed notice and must exercise reasonable care and diligence in keeping itself informed of accidents out of which claims for damages may arise. Sec. Mut. Ins. Co. of N.Y. v. Acker-Fitzsimons Corp., 31 N.Y.2d 436, 340 N.Y.S.2d 902, 293 N.E.2d 76, 78-79 (1972). A good-faith belief by the insured that an incident does not trigger coverage under its insurance policy “may excuse or explain a seeming failure to give timely notice.” Id. at 79. While the question of the reasonableness to give timely notice is generally a question of fact under New York law, “a delay may be unreasonable as a matter of law when either no excuse is advanced or the proffered excuse is meritless.” Olin Corp. v. Ins. Co. of N. Am., 966 F.2d 718, 724 (2d Cir. 1992).

Here, Lumbermen’s commercial general liability policy required Appellant, as additional insured, to give notice “as soon as practicable” of an occurrence that may result in a claim. Appellant’s three year delay in providing notice of the underlying assault is unreasonable as a matter of law. Appellant cannot claim it was unaware of the incident at the time of its occurrence because it received a report of the assault from its security company, Burns, on the day of the assault. See Travelers Ins. Co. v. Volmar Const. Co., Inc., 300 A.D.2d 40, 43, 752 N.Y.S.2d 286 (N.Y.App.Div. 2002). Furthermore, the unusual nature of one aspect of the victim’s injury, discovered fifteen months after the incident, does not alone justify delay. See Olin Corp., 966 F.2d at 723-24 (“[I]t does not follow that an insured is obligated to provide the insurer notice of an occurrence only when it learns of a particular identified injury.”). On the facts of this case, we cannot find that Appellant’s provision of notice only after initiation of the underlying lawsuit is reasonable.

For the foregoing reasons, the judgment of the district court is hereby AFFIRMED.