The irony of Jehan's genorosity
Jehan Daas is a very kind-hearted and generous man who takes in Nello after his mother dies, leaving him an orphan. Despite having few resources and being in a position where taking Nello would make his life more difficult, Jehan still takes the boy in and treats him as his own.
The irony of Aloise's love
In the time period that A Dog of Flanders depicts, people often married because of status, not because of love. That's why Aloise loving Nello is so unexpected: Nello has nothing, while Aloise comes from tremendous wealth. Still, the two fall in love.
The irony of Nello's drawing ability
One of the most important traits an artist has is the ability to write well to express themselves. Historically, there have been few artists that have not been able to draw. Despite his inability to read, Nello is a truly gifted artist and nearly wins a drawing competition.
The irony of the fire on Baas' property
One day, a fire erupts on Baas' property, destroying much of it. Nello is unexpectedly blamed for the fire, despite having nothing to do with it and despite not being near the property at the time the fire started.
The irony of Nello's death in the cathedral
Cathedrals are considered safe places in which the sanctity of life is honored (and in which no one dies). However, Nello dies in the cathedral, subverting readers' expectations.