[Your Name, & Address here]
[Recipient Name & address here]
I am sorry to know about your pet’s death.
I know there are many people who find it very foolish to mourn on death of a pet, but having known you for these years; it is understandable that how close you were to your pet. He/she was very special for you.
The [pet’s name]’s death is a personal loss to you and has saddened you a lot. He/she was a member of your family and he/she loved you a lot. You had huge love for [pet’s name] and you would do everything possible to keep him/her in a good condition.
You will miss him/her very much in the future.
I want to tell you that I am with you in this sorrowful time, please call me anytime if you feel heavy.