Geoghegan Hart follows Sir Bradley Wiggins, Chris Froome, Geraint Thomas and Simon Yates in winning one of the big three stage races on the calendar, delivering Britain's 11th Grand Tour victory since Wiggins won the Tour de France in 2012, and second in the Giro after Froome in 2018.
But this victory was by far the most unexpected entry on the list, with Geoghegan Hart having started the Giro planning to support Thomas before the Welshman's race-ending crash on stage three.
An outstanding final week in the mountains propelled Geoghegan Hart up the standings, with his victory on Saturday's stage 20 setting up the unprecedented scenario of the top two in a Grand Tour being level on time at the start of the final day.
Geoghegan Hart’s father, Tom Geoghan, was born in Scotland, with a mixed Irish/Scots heritage, and his gran still lives in Edinburgh.
The winner pulled on the pink jersey for the first time on the final podium after the race came down to two riders who began the opening stage in Sicily three weeks ago as domestiques.
"It's bizarre, to be honest," Geoghegan Hart. "Not in my wildest dreams did I imagine that this would be possible when we started nearly a month ago in Sicily.
"All of my career I've dreamt of trying to be in the top five, top ten maybe in a race of this stature so this is something completely and utterly different. I think this is going to take a long time to sink in."