Veteran actor Chen Tianwen, 52, is a late bloomer.

Largely typecast in boorish uncle roles in TV dramas, his show business career found its second wind with acclaimed local movie Ilo Ilo (2013).

In April this year, he became the accidental star of the viral music video Unbelievable, which has inspired a new movie.

He will take the lead role in a movie for the first time in the comedy titled Mr Unbelievable.

"I'm really excited and nervous. At such a late age, I get to be a movie lead and record a song," says Chen in Mandarin.

"In my younger days, whenever I sang, people would tell me not to sing and get off the stage. They said my singing was awful.

"I would never have imagined that my awful singing for Unbelievable would get such a wild reaction."

The self-deprecating actor was speaking yesterday at a press conference to announce the movie, alongside fellow cast members such as Liu Lingling, Roy Loi and Marcus Chin.

Filming has already begun and the $1-million production is slated for a December release.

The movie revolves around Chen's Ah Beng character Eric Kwek in Spouse For House, the Channel 5 drama which spawned the music video Unbelievable.

In it, the getai industry is in a bind when the government implements the Speak Mandarin campaign and discourages the use of dialects.

Kwek then comes up with the idea of changing the dialect lyrics to English.

This unconventional idea is met with resistance by his traditionalist mentor (Marcus Chin).

In real life, Chen took to the getai stage to perform last month, reportedly earning a four-figure sum for singing two songs, including Unbelievable.

"The audience was very excited when I took to the stage. When I started singing Unbelievable, people whipped out their mobile phone cameras and started filming," says Chen, who declines to reveal how much he was paid for the gig.

He adds that people in the streets now call him Unbelievable instead of his name.

In the music video, which has more than 1.9 million views on YouTube, Chen belts out cheesy lyrics such as "You blossom like a flower, I so stunned like vegetable".

The movie's director Ong Kuo Sin, who directed Spouse For House and also penned Unbelievable's lyrics, says: "It's kind of nonsensical. I was just looking for words that rhyme - unbelievable, cable, vegetable. Whatever that rhymed, I just dropped it in."

The humorous music video and tune have spawned parodies and inspired products, such as tees emblazoned with the lyrics.

The silly tune even made it to Taiwanese TV news and American magazine Time's online site.

"Last week, my older brother's maid told him that Unbelievable has been reported on the news in the Philippines," says Chen, who became a father recently and sings Unbelievable as a lullaby to his two-month-old son.

With the likelihood of snagging more singing jobs, Chen knows he could do with some vocal lessons.

He has asked his co-star Loi, a singer-songwriter, to impart some singing tips, but Loi thinks Chen is doing fine.

Loi, 50, says: "Previously, there might have been a lot of emphasis on techniques such as vibrato.

"These days, there's no fixed definition of good singing. As long as you have a distinct flavour, your own style, that's fine.

"That's the case for Unbelievable. Tianwen has his own style."