Former heavyweight champion Joseph Parker denied taking any prohibited substance and said his failed drug test from last month's loss to Fabio Wardley was “a real surprise.”

The New Zealander's voluntary anti-doping test conducted on the day of the bout returned an adverse finding, promotions company Queensberry announced on Friday.

Wardley stopped Parker in the 11th round at the O2 Arena in London on Oct. 25 in a fight to determine who would become the WBO mandatory challenger to undisputed world champion Oleksandr Usyk.

“Before my recent fight I took a voluntary test and have now been informed that it returned an adverse result. This came as a real surprise to me," Parker said early Saturday in a statement on Instagram.

“I did not take any prohibited substance, I do not use performance enhancing drugs and do not support their use,” he continued. “I am cooperating fully with the process now underway, and I am confident the investigation will clear my name.”

The 33-year-old Parker faces a potential lengthy ban by the British Boxing Board of Control.

“Thank you to everyone who has sent messages of support. It means a great deal to me and my family,” Parker’s statement added. “When the investigation is complete, I will speak openly and answer questions.”

On Friday, Queensberry said the Voluntary Anti-Doping Association had informed all parties of the adverse finding. The promotions company said it won’t make any other comments “while the matter is investigated further.”

Parker won the WBO title in December 2016 when he beat Andy Ruiz Jr. on a majority decision. He then lost the belt to Anthony Joshua by a unanimous decision in late March 2018 at the Principality Stadium in Cardiff.