Nikaah without witnesses
Q: My question is about Nikaah. One person did nikaah to woman like this. They both wrote on a paper that in the name of Allah I accept you as wife and husband. Then they speak verbally three times to each other kabool he kabool he. Then boy gives her haq mahar. Then the boy told many people he has did nikaah for gawaah or witness after some time. Is that nikaah valid?