Robert Downey Jr. doesn't just star in HTC's latest TV ad - he wrote the script

HTC has gone for a more emotional than usual approach with the TV ad for its latest flagship smartphone, the One M9 (you can watch it in full below.)

It is narrated by long-term brand ambassador Robert Downey Jr. The script aims to remind the viewer that we're "all one."

But Downey Jr. doesn't just read the script. He helped write it.

Idris Mootee, HTC's recently appointed chief marketing officer, spoke with Business Insider at Mobile World Congress in Barcelona about how the ad came about.

He told us: "I called him up and I said I want you to be our storyteller. He said 'OK, I'll do that.' And he helped write [some of the script.] I changed it, he changed it, [his wife] Susan Downey Jr. changed it. It went back and forth like this."

Then it came to recording the voiceover. Mootee admits some of his colleagues were a little nervous about the idea: HTC has a huge contract with Robert Downey Jr. and the new marketing boss didn't even want him on screen in the ad. But Mootee said eschewing the Hollywood actor and instead featuring emotive connections between lots of (unknown) people was the best way to tell HTC's brand story.

Mootee continued: "It took just one day in the studio. Afterward he called Susan and said 'it's beautiful, like a poem'. It only took three takes, 15 minutes, he loved it so much [and thinks] this is the best way to tell our story. He really believed in that and represents us."

Robert Downey Jr.: From Iron Man to Mad Man.

Here's the TV ad, which was unveiled at the HTC One M9 launch event in Barcelona on Sunday. The ad starts at around 0:05.