Yes, they're definitely fake. This is a reprint of the 'Braun diaries' originally published in 1948.
They were published by an obscure film actor named Luis Trenker who forged the diaries from memoirs written decades earlier by Countess Irma Larisch-Wallersee ; this forgery was established by the Munich courts in October 1948.
Tantalisingly, there
were some diaries, and a lot of correspondence between Braun and Hitler, believed to have been captured by a US CIC team led by Colonel Robert A Gutierrez in the Summer of 1945. These items then vanished and it is believed that they have been retained by Guttierez privately.
Sorry to add a warning here : the above information is from ( wait for it... )
David Irving ! 