The brothers, second and third in line to the throne, will sign the book at the Australian High Commission in London on Wednesday at 3.30am (AEDT).

Their aunt Princess Anne represented her mother Queen Elizabeth II at Sunday's national remembrance ceremony in Melbourne, and visited the areas affected.

Queen Elizabeth, 82, has made a private donation to a fundraising appeal helping the victims of the bushfires.

Prince Charles has also sent a message of sympathy. -- AFP