Does signing a mutual termination agreement prohibit dismissal for serious misconduct?

On January 15, 2018, the parties signed a mutual termination agreement to take effect on June 30, 2018, providing for the payment of specific severance pay.

At the end of the withdrawal period, the agreement was sent to the Direccte and was approved.

On April 11, 2018, the employee was summoned to a preliminary interview prior to possible dismissal, and was then dismissed for serious misconduct on April 23, 2018.

He brought the case before the labor court in order to obtain payment of sums in respect of the termination of his employment contract.