Daughter of Ptolemy IX
Wife successively of her uncle Ptolemy X & brother Ptolemy XI

As nominal co-ruler with her first husband she assumed the name Cleopatra Philopator (101 BCE) & accompanied him on his exile & return.  She succeeded  her father as sole ruler of Egypt (81 BCE) but was murdered by her younger brother less than a month after their arranged marriage (80 BCE). News of her murder caused riots by the citizens of Alexandria that resulted in the latter's expulsion.  

Reference: Eusebius, Chronicle: the Egyptians.

Other online resources:

• Berenice III, Ptolemy X Alexander II, Ptolemy XI (Auletes) - chapter 12 of E. R. Bevan's 1927 classic The House of Ptolemy [archived in Bill Thayer's Readings in Egyptian History].

• Berenice III of Egypt - entry in Wikipedia's web.

• Berenice III - Christopher Bennett's annotated Egyptian Royal Genealogy provides detailed references & sources.

• Berenice III - Jona Lendering outlines basic biographical data & chronicles events [Livius: Articles on Ancient History].