For instead of extolling the virtues of her education at the school, the 51-year-old former GMTV anchorwoman donned her proverbial size 10 bovver boots – and gave her old school a damn good kicking.
In front of a gobsmacked audience, Fiona accused the school of crushing her aspirations and turning her into a 'vile teenager' who was arrested for shoplifting.
She claimed that before leaving with one O-level she expressed a desire to become a doctor but was asked by teachers: "Have you thought about hairdressing?"
She described the headmaster at the time as a man who 'commanded no respect whatsoever'. And she recalled how she and her classmates locked a teacher in a cupboard and threw another over a bush.
She went on the attack at a ceremony rebranding Millbrook as the £16million Oasis Academy Lord's Hill.
"It was a school rampant with hormones and no discipline, no aspiration and no encouragement," she said.
"I can remember being in classes throwing furniture around. We locked a fashion teacher in a cupboard and threw one over a bush, and that was normal behaviour.
"My mother was in despair because I was so vile to her. They used to come and pick me up from the police station after I had been caught for shoplifting. I was in fights after school – I won't even go into what else went on."
She said her mother could not believe that her conscientious daughter had 'turned into this vile teenager'.
"I left with one O-level in English language, purely because I read a lot and all my education came from home," she said.
Fiona added: 'I'm proud to say I went to Millbrook School. I'm not proud of the education I had there."
She added that she was angry the Millbrook area had seen 'hardly any investment in nearly half a century'.
Her harsh remarks upset many of those connected with the school, with the Mayor of Southampton, Derek Burke, a former governor of Millbrook, accusing Fiona of 'dramatic licence'.
He added: "It wasn't nearly as bad as she painted it."
After leaving, Fiona worked for a short time at Mr Kipling's bakery in Eastleigh, but decided to give education another try and gained a BA in English at Birmingham Polytechnic. She began her journalistic career at independent local radio stations in Sussex.
If you were invited to give a speech at your old school, what would you say?