EXCLUSIVE: Valerie Harper rushed to hospital, 'it doesn't look good,' source says

Valerie Harper suffered a health emergency Wednesday night, when she was taken away by ambulance during a performance of her musical Nice Work If You Can Get It at the Ogunquit Playhouse in Maine.

The fire department confirms to ET that they received a call at 8:56 p.m. about an unconscious 75-year-old female backstage, and that she was taken to York Hospital. According to Ron Corning, anchor and correspondent at ET's affiliate in Dallas WFAA, around 9:40 p.m., the artistic director of the musical announced to the audience that the ambulance seen on the side of the lawn was for the 75-year-old actress, and that she had fallen ill and wouldn't be performing.

Photos of Valerie Harper from over the years:

The director then said, "She wants all of you to know after some fluids and rest she hopes to be right back here on stage later this week."

However, a source close to the situation tells ET, "Just know it's very bad."

Corning also spoke to the art tech on site, who said that Valerie has not been well all week.

The Mary Tyler Moore Show star only appears in the second act of the play, and is set to perform through August 15.

Valerie was diagnosed with terminal brain cancer in 2013, after previously beating lung cancer in 2009. In April, she told ET that her cancer has not spread to other parts of her body, though pointed out that contrary to reports, she has not been "cured."

"In a way, it's a positive thing to know that a year's gone by and it's nowhere else in my body," she said. So I am cancer free from the neck down, so far."

Watch below as Valerie sets the record straight on her cancer diagnosis: