Is it permissible to financially assist one's former wife many years after their divorce, and would this assistance be considered sadaqah (charity) or zakat, especially given the current wife's jealousy?

Assisting Muslims and fulfilling their needs is an aspect of excellent Islamic conduct and perfect character. This is supported by verses and hadiths, such as the Almighty's saying: "Indeed, Allah enjoins justice and good conduct," and the Prophet's (peace and blessings be upon him) saying: "Whoever among you is able to benefit his brother, let him do so."

Therefore, it is preferable to help the ex-wife while concealing this from the current wife to avoid problems. If the ex-wife is poor and has no one to support her, then it is permissible to give her from zakat; otherwise, it is not.