If a person divorces his wife without presence of anyone else it is valid?
in other words
Is a divorce (Talaq) valid without any witness?
Not it is not valid as Quran says:
فَإِذَا بَلَغْنَ أَجَلَهُنَّ فَأَمْسِكُوهُنَّ بِمَعْرُوفٍ أَوْ فَارِقُوهُنَّ بِمَعْرُوفٍ وَأَشْهِدُوا ذَوَيْ عَدْلٍ مِّنكُمْ وَأَقِيمُوا الشَّهَادَةَ لِلَّهِ ۚ ذَٰلِكُمْ يُوعَظُ بِهِ مَن كَانَ يُؤْمِنُ بِاللَّهِ وَالْيَوْمِ الْآخِرِ ۚ وَمَن يَتَّقِ اللَّهَ يَجْعَل لَّهُ مَخْرَجًا (طلاق/2)
Then, when they have reached their term, retain them honourably, or part from them honourably. And call in to witness two men of equity from among yourselves; and perform the witnessing to Allah Himself. By this then is admonished whosoever believes in God and the Last Day. And whosoever fears Allah, He will appoint for him a way out,