In California Shoppers, Inc. v. Royal Globe Ins. Co. (1985) 175 Cal.App.3d 1, an action by an insured against its insurer for breach of the contractual duty to defend, the insurer was held to have had constructive notice of tender of the defense when the insured sent to the insurer a copy of the summons and complaint naming the insured as a defendant, notwithstanding an envelope with the return name and address of another entity, also an insured under another policy but not named in the enclosed complaint, and the lack of a cover letter. The court concluded that, had the insurer made diligent inquiry, it would have concluded that tender came from the insured and not the other entity. The court summed up: "In other words, given the appropriate circumstances, the law will charge a party with notice of all those facts which he might have ascertained had he diligently pursued the requisite inquiry." (Ibid.) The concept of constructive notice was also developed in Truck Ins. Exchange v. Unigard Ins. Co. (2000) 79 Cal.App.4th 966, an equitable contribution action between coinsurers. In Unigard, the defendant, Unigard Insurance Company, did not participate in the underlying litigation due to a lack of tender by its insured. The plaintiff, Truck Insurance Exchange, gave notice to Unigard of its potential liability for equitable contribution only after the underlying litigation was resolved. the question presented was "when does an insurer that is providing a defense have to raise the issue of contribution with potential coinsurers that are not participating in the litigation due to a lack of tender." (Unigard, supra, 79 Cal.App.4th at pp. 978-979.) The Court rejected Truck's argument that, regardless of when it learned the identity of potential coinsurers, notice to potential coinsurers was not necessary until the underlying action had concluded. the Court determined that notice should be given sooner, rather than later. (Id. at p. 979.) "Under these circumstances, the imposition of contribution on Unigard--a stranger to the litigation--would subject it to a significant financial burden even though it did not enjoy any of the concomitant benefits, e.g., the right to participate in and control the defense. Truck decided to investigate and settle the underlying litigation without Unigard's involvement. Having done so, Truck should not be permitted to drag Unigard into the picture after the fact. ... With prompt notice, the coinsurer can investigate the matter and decide whether to join in the defense. If, however, notice is given after the underlying litigation is over, the matter is more likely to end up in court." (Id. at pp. 979-980.) In Unigard we thus concluded that "the notice should have been made promptly after Truck agreed to provide a defense. That is not to say that Truck had to tender the defense to Unigard. a simple notice regarding the possibility of contribution would have been sufficient." (Unigard, supra, 79 Cal.App.4th at p. 982.)