Team Sky's star became the first Brit to win the Giro d'Italia in May and built specifically for the Tour de France, where he already won four times before. However, he was slightly off his best. Assuming all ends well in Paris tomorrow, he managed third overall behind Sky team-mate Geraint Thomas and Tom Dumoulin (Team Sunweb) in second.
"I still believe it's possible to do the double," Froome said. "I've won the last three consecutive grand tours now and should be third tomorrow if nothing goes wrong, so I still believe it's possible. It's not going to be this year that's for sure."
Froome is the latest who has given the double a go in recent years, and came very close to pulling it off. Froome won the Giro and moved to third in the Tour on stage 20, a place to be confirmed after the flat stage in Paris on Sunday.
In 2017 Nairo Quintana in 2017 placed second in the Giro and 12th in the Tour, and in 2015 Alberto Contador won the Giro and placed fifth in the Tour.
Only seven riders have won the Giro and Tour in the same season. In 1998, Italian Marco Pantani conquered his home tour before going on to win the French Grand Tour that was hit with the Festina scandal.
Watch: Tour de France 2018 stage 20 highlights
Froome fell off the mark, but came close. So did Dutchman Tom Dumoulin, who placed second in the Giro and defended his second place in the Tour with the time trial stage win on the penultimate day.
"It's interesting that you brought up Tom," Froome told journalists. "For him to be second in both Grand Tours shows that it's possible to do both of the races at a high level, which leads me to believe it is possible to do both of them.
"It was big factor to do the Giro this year with the extra week off thanks to the World Cup. That was part of my decision. As I said, I still believe it's possible, but it's going to take some doing."
Froome counts six Grand Tour wins. After the 2017 Tour victory, he won the 2017 Vuelta a España and this May, the Giro. It is assumed he will spend time at home with his family with his wife due to give birth to their second child in the coming days, and not race the Vuelta a España starting in August.
As for the 2019 season, Froome says that he is still to consider his targets for next year.
"It's too early to think that far ahead, we haven't seen what the parcours looks like," Froome continued.
"I'm mostly just thinking about getting home to the birth of my second child now, which should be any moment now. And take it from there and plan for the rest of the season. I'm not writing anything off and taking any decisions at this point."
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