Lili Reinhart has been diagnosed with endometriosis.

Taking to Instagram on Thursday, the Riverdale actress shared two photos showing her lying in a hospital bed.

In the accompanying caption, Lili explained that a doctor recently diagnosed her with adenomyosis - a condition where the lining of the uterus starts growing into the muscle in the wall of the womb.

And following laparoscopic surgery last week, the surgeon confirmed she had endometriosis, a chronic disease where tissue similar to the lining of the uterus grows in other parts of the body, such as the ovaries and fallopian tubes.

"Last week, I was officially diagnosed with endometriosis following laparoscopic surgery. It wasn't until I worked with two different pelvic floor therapists that the word endometriosis was even mentioned to me as a possible source of my pain," she wrote. "I pushed for an MRI on my own, which led to a diagnosis of adenomyosis. From there, I met with an endometriosis specialist who helped me decide that laparoscopic surgery was the next step I wanted to take."

Lili went on to note that multiple doctors had dismissed her symptoms, with a gynaecologist even telling her that she "probably didn't have" endometriosis and that she should "just go on the (birth control) pill".

The Hal & Harper star was even diagnosed with interstitial cystitis by a urogynecologist at one point and told there was "no cure".

"Three hospital visits. Multiple urologists and gynecologists. And not one of them seriously considered endometriosis as the underlying cause of what I was experiencing," the 29-year-old added. "I'm glad I trusted my body and listened to my gut and will continue advocating for others to do so."

Following the health update, Lili was inundated with supportive messages from her celebrity friends.

"Love you so much lils," commented her Riverdale co-star Madelaine Petsch, while Rachel Zegler posted, "The medical gaslighting of women in particular is so crazy!!!! thank you for sharing your story!!!!!!!"