Thomas, a two-time Olympic champion for Great Britain in track cycling before turning his full attention to the road, took it all in his stride and after dominating the mountain stages in the Alps with two superb victories, maintained his advantage in the Pyrenees and on the final time trial to hold off his closest rivals for the prized crown in cycling.
Coming home second by a margin of one minute, 51 seconds was Tom Dumoulin ahead of pre-tour favourite Froome and LottoNL-Jumbo's Primoz Roglic.
Thomas may have known he had a buffer to play with, but he was not taking it easy as he was fastest through the first and second splits before grinding up the Col de Pinodieta and dropping back.
Thomas was a support rider during Froome's title rides but he became Sky's undisputed leader when Froome cracked in the grueling 17th stage through the Pyrenees. "Respect to him for that because it must have been hard having a team-mate getting the plaudits and wearing the [yellow] jersey sat on the bus next to him".
The Welshman's triumph is the sixth by a British rider since 2012 and saw him beat his team-mate and compatriot Chris Froome, the victor of four of the past five instalments of the three-week stage race.
"He didn't make any mistakes, he was never put into trouble by anyone - including me - in the mountains or in any stage".
Egan Bernal finished far off in second, but the Colombian sensation was effectively prevented from competing for the white jersey due to his duties in helping Team Sky's Geraint Thomas win the yellow jersey.
"I guess it (helped)", he said of Froome's time loss.
Norwegian rider Alexander Kristoff with UAE Team Emirates won the last stage in a sprint finish, narrowly beating John Degenkolb and Arnaud Demare.
"If someone told me, after such a hard Giro, that I'd win a stage at the Tour and finish second, I'd have signed". It's just incredible. The last time I cried is when I got married.
"I felt strong. I felt really good, actually". Team Sky chief Dave Brailsford has seen Thomas go from being dropped every day on his maiden Tour, when he was the youngest to start in 2007, to conquering the race 11 years later. I tried not to think about it, just take it day by day.
He'll also be the first rider from Wales to win the race.
"To win on Alpe d'Huez in the yellow jersey". "When he was with me full-time, we lived in Manchester or in Italy".
Four-time champion Froome crossed the line with Thomas and applauded him. According to Ellingworth, that victory ahead of two-time Tour de France victor Alberto Contador was a turning point.
With his title, Thomas joins rugby's Sam Warburton and football's Gareth Bale in the Welsh sports half of fame as all three of them were educated at Whitchurch high school.
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