Ballsy Springboks strip-down for testicular cancer

South Africa's wing Cheslin Kolbe (C) kisses the Webb Ellis Cup beside South Africa's scrum-half Faf de Klerk (L)

Rugby World Cup-winning Springboks have stripped down to their underwear in response to a challenge by scrumhalf Faf de Klerk for South African men to get screened for testicular cancer.

Captain Siya Kolisi, wingers Cheslin Kolbe and Makazole Mapimpi were among players to slip into their speedos and post pictures in their underwear on social media after being screened, in response to the now viral #FafChallenge.  

"Challenge accepted!.. Early detection = high cure rate," Kolisi wrote on his Instagram page where he posted a picture of himself sporting South African flag-branded underwear.  

Kolbe responded saying, "what's more awesome than scoring the final try in the Rugby World Cup? Ensuring that you're healthy." 

"Don't wing it when it comes to testicular cancer. Catch it early!" Mapimpi wrote. 

De Klerk, 28, initiated the #FafChallenge online on Wednesday, posting a picture of himself flaunting his now famous South African flag-themed underpants.

He instantly became an internet hit after he was photographed greeting Prince Harry in the pants just moments after their World Cup victory against England in Japan.

"Be ballsy enough to check your balls!" he told his more than 36,500 followers on Twitter.

"Challenging Siya, Jesse, and all of you to get into your speedo & post a pic to help spread the word on this important cause!"

The disease is one of the most common cancers in men aged between 15 and 39 years.

De Klerk told a local rugby magazine that he was surprised by the public reaction to his underpants.

"There is no massive back story. I just always play in a South African speedo when I play for the Springboks. I've probably played the last two years with it," he was quoted as saying by SARugbyMag.

The Springboks beat England 32-12 victory against England in Japan on November 2, earning their third world crown in rugby's paramount tournament.