When anonymous letters were posted to a local newspaper announcing a plot to shoot her with a crossbow, the 81-year-old mocked the sender during an appearance at the country's National Day celebrations.
Provocatively waving an apple in the air, the doughty octagenarian showed no sign of fear as she viewed the traditional military parade at the Royal Palace in Brussels.
The gesture, a reference to Swiss folk hero William Tell who shot an apple off the head of his son, sent a ripple of laughter through the crowds.
Supporting her at the procession, her nephew Crown Prince Philippe and his glamorous wife Mathilde also had to chuckle at her boldness.
Her response was even more surprising given that earlier this year a serious bout of pneumonia put her in hospital.
Fabiola, the widow of Philippe's late uncle King Baudouin, is popular in the country because of her tireless work for children's charities.
Royal officials have now upped security measures surrounding her, with police helicopters, extra officers and police dogs deployed around the Palace for this week's festivities.