Dynamically create an entity instance and add a new entry

Please, consider the following example:

public override int SaveChanges()
{
    foreach (var auditableEntity in ChangeTracker.Entries<ISomething>())
    {
        if (auditableEntity.State == EntityState.Added)
        {
            //Create a new instance of the same entity type. 
            //I don't know which one will be. They just have the same interface.
            var newEntity = ?; //???Reflection???

            //ISomething known properties.
            newEntity.propX = "1";
            newEntity.propY = "2";

            //Invoke Add method.
            ??.Add(newEntity); 
        }
    }

    return base.SaveChanges();
}

I need to dynamically create an instance of all my ISomething entities during SaveChanges() method in order to add a new particular entry on it.

Any help will be very welcome.

Regards