The campaign is appealing to 125,000 existing donors at the beginning of November, followed by a second mailer in December.
The mailer will include two gifts: a calendar with an illustration and description of an animal that has been cared for by the charity; and a bookmark illustrated by a cat on one side and a dog on the other, with a short poem written from the animal's perspective.
Instead of last year's focus on older pets, Clement forms part of a campaign to urge donors to offer cash gifts of £15, £30, £50 or an amount of their choice.
The mailer features a photograph of the dog next to the text "Please make this Christmas special for those that need your help the most."
Inside, the letter reads: "This Christmas, will you please give lonely pets like Clement the chance to be loved again?"
The mailer goes on to describe the work that the charity does by providing a safe home for unwanted pets over the Christmas period and throughout the year.
Julie Jeffes, head of marketing at The Blue Cross, said: "Christmas marks a busy time for The Blue Cross, with a sharp rise in the numbers of animals being cared for at our adoption centres.
"Whether they are an unwanted Christmas gift or an older pet whose owners can no longer care for them, The Blue Cross makes every effort to re-home them with loving owners."
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