Rome (AFP) - Britain's Chris Froome completed a sensational comeback to win the Giro d'Italia on Sunday for a rare Grand Tour treble which could be in danger if he is sanctioned by anti-doping authorities.

Froome, 33, became the first Briton to win the race in the Giro's 101-year history after a 115km closed circuit race through the streets of the Italian capital.

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But his presence was not without controversy as he was competing despite an ongoing investigation after returning an adverse analytical finding during his Tour of Spain win last year.

His triumph on Rome's Imperial Forums, where Ireland's Sam Bennett took the 21st and final stage, capped a long chaotic journey for the Briton. 

From the departure in Jerusalem, a historical novelty of this Giro, to the Alps of Piedmont and Valle d'Aosta, the four-time Tour de France winner endured what he called "the greatest battle of my career".

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Sitting fourth overall three days before the finish, Froome seized the race leader's pink jersey on Friday after capping a 80km solo breakaway with a stage win, and held it all the way to Rome.

Froome is now the reigning champion in all three of cycling's Grand Tours -- the Giro d'Italia, Tour de France and Tour of Spain -- and becomes only the third rider to achieve the feat after Belgian Eddy Merckx (1972/73) and
France's Bernard Hinault (1982/83). 

"I'm still pinching myself. I can't believe I'm here," said Froome. "This is the dream to have all three jerseys in the space of ten months. It's an incredible feeling."

'A bit afraid'

Froome finished 46sec ahead of defending champion Tom Dumoulin (Sunweb) of the Netherlands in the overall standings, with Colombian Miguel Angel Lopez (Astana) third at 4min 57sec.

"I don't think it's quite sunk in yet. I hope it will over the next three days," added Froome, who was competing in the Italian race for the first time in eight years.

"I've always been a bit a afraid of coming here. The demands of the race are so different than any other race. To be here and to have won it I can't quite believe it." 

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Bora rider Bennett sprinted to victory in the 21st and final stage, his third of this year's race, after pipping four-stage winner Elia Viviani (Quick Step) at the line.

Froome's maiden Giro triumph has also set up the possibility he could target a rare Giro d'Italia-Tour de France double in the same calendar year -- last achieved by Italian rider Marco Pantani in 1998.

But his stunning success is partly overshadowed by controversy as the British rider continues to compete despite an ongoing anti-doping investigation.

Froome provided an adverse analytical finding in his urine for double the permitted amount of the asthma drug salbutamol when he won the Tour of Spain last year.

The Briton has a Therapeutic Use Exemption (TUE) allowing him to use salbutamol and escaped a provisional suspension, although the case has yet to be resolved by cycling's world ruling body the UCI.

His victory was nevertheless impressive. Froome fell twice including before the first stage and at one point trailed the leaders by nearly five minutes.

But he powered back in the final week, winning two mountain stages including the prestigious 14th stage to the summit of Monte Zoncolan. 

His memorable solo effort on stage 19 was pivotal, Froome taking the pink jersey after long-time leader and fellow Briton Simon Yates (Mitchelton) suffered a stunning collapse.

The Tour de France winner put himself on the brink of victory in the 20th and penultimate stage when he led Dumoulin by 46 seconds.

And he defended his overall lead Sunday through the essentially flat streets past some of Rome's iconic landmarks.

"It's great to be able to soak up the atmosphere on the road, the mouments and the crowds," said Froome of the stage which neutralised with seven laps to go for security reasons leaving him to just cross the line to ensure victory.