Seventy four year old Oleksiy Vadatursky, and his wife Raisa died when a missile hit their home overnight.
Vadatursky owned Nibulon, a company involved in grain exports.
Mykolaiv mayor,Oleksandr Sen-Kevych said it was probably the heaviest Russian bombardment of the city so far.
There was damage to a hotel, a sports complex, two schools and a service station, as well as homes.
Mykolaiv is on the main route to Odesa, Ukraine’s biggest port on the Black Sea, and has been hit repeatedly since Russia launched its invasion on 24 February.
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