Ordered that the order is reversed insofar as appealed from, on the law, with costs, and the plaintiff's motion for summary judgment on the complaint is granted.
Insurance Law § 3420 (d) (2) states that written notice of a disclaimer shall be given "as soon as is reasonably possible" after the insurer learns of the grounds for disclaimer of liability or denial of coverage ( see First Fin. Ins. Co. v Jetco Contr. Corp., 1 NY3d 64; Matter of Firemen's Fund Ins. Co. of Newark v Hopkins, 88 NY2d 836, 837; Varella v American Tr. Ins. Co., 306 AD2d 464). "An insurer's failure to [timely disclaim liability or deny coverage] `precludes effective disclaimer or denial,' even where the insured and the injured party have failed to provide the insurer with timely notice of the claim in the first instance" ( Matter of Allstate Ins. Co. v Cruz, 30 AD3d 511, 512, quoting Hartford Ins. Co. v County of Nassau, 46 NY2d 1028, 1029 [citation omitted]).
The plaintiff submitted an affidavit of service by mail dated February 12, 2003, stating that service by mail was made that day of a judgment with notice of entry. The judgment had been entered in his favor and against the defendant's insured on February 10, 2003. This raised a presumption that a proper mailing occurred. In opposition, the defendant's papers failed to raise a triable issue of fact regarding service of the judgment ( see Kihl v Pfeffer, 94 NY2d 118, 122; Engel v Lichterman, 62 NY2d 943, 944-945; Kendall v Kelly, 283 AD2d 401).
In addition, under the facts and circumstances of this case, the defendant's 51-day delay before disclaiming coverage on April 4, 2003, on the ground of late notice of the underlying lawsuit, was unreasonable as a matter of law ( see First Fin. Ins. Co. v Jetco Contr. Corp., 1 NY3d 64; Sirius Am. Ins. Co. v Vigo Constr. Corp., 48 AD3d 450; Reyes v Diamond State Ins. Co., 35 AD3d 830; Matter of Allstate Ins. Co. v Swinton, 27 AD3d 462; Moore v Ewing, 9 AD3d 484). Accordingly, the plaintiff's motion for summary judgment on the complaint should have been granted ( see Varella v American Tr. Ins. Co., 306 AD2d 464). In view of this determination, it is unnecessary to reach the plaintiff's remaining contentions.