paragraph: Alexander fled Macedon with his mother, dropping her off with her brother, King Alexander I of Epirus in Dodona, capital of the Molossians. He continued to Illyria, where he sought refuge with the Illyrian King and was treated as a guest, despite having defeated them in battle a few years before. However, it appears Philip never intended to disown his politically and militarily trained son. Accordingly, Alexander returned to Macedon after six months due to the efforts of a family friend, Demaratus, who mediated between the two parties. In the following year, the Persian satrap (governor) of Caria, Pixodarus, offered his eldest daughter to Alexander's half-brother, Philip Arrhidaeus. Olympias and several of Alexander's friends suggested this showed Philip intended to make Arrhidaeus his heir. Alexander reacted by sending an actor, Thessalus of Corinth, to tell Pixodarus that he should not offer his daughter's hand to an illegitimate son, but instead to Alexander. When Philip heard of this, he stopped the negotiations and scolded Alexander for wishing to marry the daughter of a Carian, explaining that he wanted a better bride for him. Philip exiled four of Alexander's friends, Harpalus, Nearchus, Ptolemy and Erigyius, and had the Corinthians bring Thessalus to him in chains. 
question: Why did Olympias and several other friends of Alexander, think that Philip intended to make Arrhidaeus his heir?
answer: Demaratus mediated between the two parties