It was announced last month that the 25-year-old wing had failed a test for an unspecified banned substance during a July training camp with the national side.

His B-sample has now also failed for banned steroids metandienone, methyltestosterone and LGD-4033, the South African Institute for Drug-Free Sport (SAIDS) said.

Dyantyi, named as World Rugby's breakthrough player of the year in 2018, has denied wrongdoing.

"Mr Dyantyi has now been formally charged with a doping offence for multiple anabolic steroids and metabolites," SAIDS said in a statement. 

"The charge has been communicated to the South Africa Rugby Union, World Rugby and the World Anti-Doping Agency."

Dyantyi, who is now facing a ban, plays for Johannesburg-based Super Rugby club side Lions and made his South Africa debut against England last year.

He has gone on to score six tries in 13 matches for the Springboks. 

In a statement after his first failed test he claimed he had "never cheated and never will" and vowed to prove his innocence.

He now has the option to appeal.

The wing was not named in South Africa's squad for the Rugby World Cup in Japan, which begins on September 20, as he reportedly had a hamstring injury.

"SA Rugby, the Lions Rugby Company and Dyantyi are working with SAIDS, the World Anti-Doping Agency and all other relevant authorities on the matter and no further comment can be made at this stage," South African Rugby said.