In Islam, man is not permitted to sit in private or Khalwah, with his ex-wife who has been irrevocably divorced. Islam considers their meeting without a Mahram, and in private a form of illicit Khalwah, which is forbidden. However, there is nothing wrong with them meeting in a public place as long as both of them adhere to the Islamic decorum and stick to that which is lawful.
The erudite scholar, Sheikh Yusuf Al-Qaradawi, states the following: “If the woman is irrevocably divorced and her waiting period or `Iddah ends, her husband is considered a foreign man to her as other non-Maharem men.
It is permissible for them to meet together but not in private (i.e. the Mahram must be present). The Prophet, peace and blessings be upon him, is reported to have said, “When a man and a woman are together alone, the Satan makes their third.”
Thus, away from illicit privacy or Khalwah, the woman is allowed to meet her ex-husband as she meets other men as long as she sticks to the Islamic dress code, meets him in a public place, without exposing her adornment, and both parties are keen not to commit something Haram.”