I believe this watch was featured in a watch blog sometime last year. The movement in the watch has 'appeared' in a number of other brand watches from the same 'era' i.e. early 1900, with some claiming the watch is from 1880. This is difficult is substantiate although it is believed that GP did issue wristwatches as early as 1880s. The first true wristwatch was issued by PP, but it was a ladies watch and the first true mens watch was the Santos watch issued by Cartier in 1904 (or there about).
The serial number given for the watch/ movement puts it around 1970s (based on AP production numbers and serial number database, which is unofficial). I have seen similar movement by Audemars, Piguet & Co used in pocket watches, but never in a wristwatch. I am not saying that the watch is not original, but would require more proof of its authenticity. Perhaps your friend can contact AP via their website and provide them the details and pictures of the watch for verification. Here is the link (mods, please delete if not appropriate):
http://www2.audemarspiguet.com/customer_service/home/instructions/modeles_anciensAll the best.