This is the Mausoleum of the spiritual leader of the Ismailis, a Shi'ite sect (as were the Fatimid) Sultan Mahommed Shah, Aga Khan III.
The Mausloleum is on the west bank of the Nile in Aswan and used to be open to the public, I remember visiting it many years ago. It has unfortunately been closed due to damage caused by tourism.
Aga Khan III was extremely wealthy. In fact, his people say that on his birthday in the year 1945 he was weighed in diamonds, which he then gave to his followers in a spirit of generosity.
The mausoleum was built according to his wife Yvette Blanche Labrousse’s (Mata Salama) wishes. After Aga Khan’s death, his surviving widow continued to leave a red rose on his white Carrara marble tomb. Living in the villa, she managed to do this faithfully until her own death in 2000. Even to this day, as per request of Mata Salama, a red rose still finds its way to the sarcophagus.