But for Froome, the day's good work was undone in the space of a few hundred metres as he finished seventh, 20 seconds behind Aru, surrendering his general classification lead and the yellow jersey to his Italian rival. But what were the full standings after stage 12 at the 104th edition of the Tour and how do the various classifications now look?
Both riders gradually dropped back after the intermediate sprint, with Belgium's Thomas De Gendt and then Britain's Steve Cummings breaking clear of the group to pursue a potential stage win. "I'm delighted to wear this jersey, it repays all my team-mates who've helped me so much in this Tour - I dedicate it to them".
AG2R La Mondiale's Bardet timed his attack to perfection, taking victory ahead of Aru and Colombian Rigoberto Uran of Cannondale-Drapac, both two seconds back but each picking up bonus seconds.
"Today was a chance, I just needed the right combination", the 36-year-old said.
It is the first time in his career that Froome has lost the yellow jersey mid-race, having carried it all the way to Paris once he had taken it in each of his three Tour wins to date. Martin moved up to fifth in the GC at the expense of Aru's Astana team-mate Jakob Fuglsang, who struggled one day after fracturing bones in both his elbow and wrist following a crash in the previous stage.
Cummings had a two-minute lead at the top of Port de Bales and went all out in the descent as the fog broke and the weather picked up. "I put my efforts towards Sunday's stage this week, so it has come a little bit early" - Bardet may have surprised himself with the stage win.
The Colombian Nairo Quintana, he has been distanced from the slopes of the Peyresourde.