Is it legal to be fired on the spot after four years without notice?

This is very unlikely to be lawful as described. Under Article 36(5) of the Employment and Industrial Relations Act, Chapter 452 of the Laws of Malta, an employee with your length of continuous service is entitled to a statutory minimum notice period before termination, which increases progressively with years of service, and dismissing you immediately without that notice or a payment in lieu of it, and without a valid reason such as gross misconduct, is generally treated as unlawful. If redundancy is the real reason, Maltese law also requires that redundancies follow the 'last in, first out' principle within the affected category of employment, meaning the most recently hired employee in that role should generally be let go first, unless a specific lawful exception applies. You should request the employer's reasoning in writing and gather your employment contract and any relevant correspondence. If notice or a valid reason was not properly given, you can file a complaint with the Department of Industrial and Employment Relations or bring a claim before the Industrial Tribunal, which handles unfair dismissal and wrongful termination cases in Malta.