Earlier today, Maria Sharapova said on Twitter that she'd be holding a press conference at 12 p.m. PST, but it was unknown what for. It turned out she was announcing that she failed a drug test back in January at the Australian Open.

The 28-year-old tennis icon said she was notified by the International Tennis Federation that she tested positive for a banned substance, but does not yet know what her penalty will be.

"I take great responsibility and professionalism in my career every day. I made a huge mistake," Sharapova said. "I let my fans down. I let my sport down."

"I know with this that I face consequences," she continued. "I don't want to end my career this way, and I really hope I'm given another chance to play this game."

The five-time major champion has not competed since falling to Serena Williams in the quarterfinals of the Australian Open.

Sharapova tested positive for a drug called Meldonium, which was added to the World Anti-Doping Agency's (WADA) of illegal drugs on Jan. 1, but she said she was unaware of the rule change. She added that she had been (legally) taking the drug for 10 years in order to address numerous health issues (frequently ill with the flu, irregular EKGs and evidence of diabetes). The WADA said Meldonium shows "evidence of its use by athletes with the intention of enhancing performance."

The drug is manufactured in Latvia and is not approved by the United States' Food and Drug Administration.

Injuries have hindered Sharapova from competing over the past year (on top of many others in the past), which will perhaps raise speculation regarding her use of the newly banned substance. However, she should be fine as long as there's proof of her taking it for as long as she says she has.

The Russian native is ranked No. 7 in the world by the Women's Tennis Association. She's also been the highest-paid female athlete for 11 straight years.