Both parties were in the park on Rue Grand-Duchesse Charlotte in Ettelbruck, at 6.30pm.
The situation quickly became aggressive, as one of the men attacked the other with a knife, stabbing him in the leg.
The aggressor fled the scene, escaping an intensive search which followed the attack. The victim was taken to hospital to treat the wounds, which were not thought to be life-threatening.
It transpired that the victim was the new boyfriend of the attacker's ex-partner.
The investigation uncovered the identity of the alleged attacker and he was arrested at his home on Friday morning.
Later that day, the man was brought before the investigating judge to answer charges.
