What is the ruling regarding my wife's second marriage, and what should I do about it, knowing that I took her back after the second divorce, and the return was in secret, then she got married thinking that the return did not take place?

The most beloved of deeds to Iblis is causing separation between spouses, and divorce destroys families, so one must be deliberate in it.

In matters of disagreement regarding divorce, it is necessary to adopt the fatwa of someone whose religion and knowledge are trusted.

What the scholar said, that divorce does not take effect on the divorced woman and that intercourse is considered a return (to the marital relationship), is the opinion of some scholars.

Informing the wife of the fatwa and having witnesses to the return is considered an explicit declaration of return. It is not a condition to inform the family or for the wife to consent to the return.

It is recommended to inform the wife of the return and to have witnesses to it to prevent disputes. You should present the matter to the Sharia court with the fatwa and the two witnesses to confirm the return. If you do not wish to return to her, it is not permissible for you to remain silent about the matter. You can divorce her after regularizing the situation.