See their emotional first meeting.

Last month, Erich Voigt, MD, an ear, nose and throat surgeon in New York, was watching TV, tuned in to HGTV's Beachfront Bargain Hunt. But instead of checking out the tropical homes, he was drawn to show guest Nicole McGuinness. After noticing an unusual lump on the 32-year-old's neck, he sent a Facebook message with an alarming warning.

“I am watching a tv show and notice this woman has a left thyroid mass,” he wrote in a post shared with friends. “She needs a sonogram and fine needle biopsy. I wonder if she knows and hope it’s benign. #beachfrontbargainhunt.”

The message managed to get to McGuinness, who visited a doctor and was diagnosed with thyroid cancer. This wasn't her first bout of the disease; she had previously battled stage 4 glioblastoma, an aggressive, life-threatening brain tumor.

Earlier this week, Dr. Voigt and McGuinness met for the first time on Good Morning America. There, he talked about why he decided to speak up and reach out on social media.

“It just caught my eye and I knew it wasn’t right,” Dr. Voigt said, later adding, “I felt obliged to help.” Both doctor and patient were emotional in the interview, and McGuinness took the opportunity to thank him for his life-saving diagnosis.

“I never expected to have to be a two-time cancer survivor, but without you keeping a vigilant eye and watching that television show, who knows how long I would’ve gone on without that being checked? So, from the bottom of my heart thank you so much,” she said on GMA.

Dr. Voigt also shared advice on how to spot a potentially serious thyroid tumor. “Most people are in tune with their bodies, know their bodies and sometimes they may know their bodies better than their own doctor,” he explained. “So, if there’s a change—if you notice a lump, a swelling, if there’s a change in your voice, hoarseness, if you have pain—those are some subtle signs that there may be something going on.”

Though cancer is rare in young people, most thyroid cancer patients are younger than 55, and women are more at risk than men. McGuinness said she’s now seeking treatment at Duke University and intends to fight her second cancer diagnosis hard.