Is one talaq valid if the man had no knowledge or intention of irrevocable talaq?

A man gave 3 talaqs to his wife, under a lot of pressure and against his will. But he did not know that 3 talaq should not be given at once. He always thought that for talaq to happen, it has to be said 3 times otherwise talaq doesn’t happen. A few weeks after giving talaq, when he consulted someone, he then got to know that even saying talaq 1 time would be enough. At the time of giving talaq the man had no knowledge that giving 3 talaq is irrevocable. He never had the intention to give irrevocable talaq to his wife. In this case, can it be considered only 1 talaq since the man had no knowledge and no intention?