A will need not be probated. The power of an estate trustee derives from the will itself. However, in certain cases, a grant of probate (now awkwardly called a certificate of appointment of estate trustee with a will) is needed and the estate trustee will have no choice but to apply for probate and to pay the accompanying estate administration tax. For example, to sell a house on the open market requires probate to assure the buyer that she is, in fact, dealing with the personal representative of the estate and buying the house from the estate (i.e. the sale is bona fide).
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