Cameron Mathison shared an update on his health on "Good Morning America" on Monday after undergoing surgery for a 4.2 centimeter mass on his right kidney "consistent with renal cell carcinoma."

The actor, host and "GMA" contributor, who was told by doctors that the tumor was likely growing inside his kidney for the last eight to 12 years, said he is "doing so, so well" after surgery in September.

"I feel great. It's about nine weeks out now from my surgery and the energy is coming back -- the strength's coming back -- but in the grand scheme of things I just feel so lucky and so good," he said.

Mathison said post-surgery that doctors were able to completely remove the tumor, and he is now left with 80% of his right kidney. He added that he is "so lucky" that his medical team caught the tumor before it went into his lymph nodes, so he will not have to undergo chemotherapy or radiation.

The actor also spoke about how he had an inkling that something was off with his health leading up to discovering the tumor.

"I have always been a healthy guy or been in touch with how I feel and what I eat -- how my body reacts -- and I really try to pay attention to my health, and, over the years, just certain things weren't right," he said.

"I had seen several doctors -- both traditional and alternative medicine doctors. I had gotten a slew of tests showing low immune function, showing a low white B blood cell count -- things that didn't make sense to me considering I eat so healthy and am active," he added.

These thoughts led him to request an MRI in his gastrointestinal area, even though he said his doctors really did not think he needed it and advised other solutions. "I got the MRI, and it probably saved my life," he said.

Mathison said he hopes people will learn to pay attention to their health and their bodies through his own story.

"My message really is to pay attention, to be mindful, to listen to your body," he shared. "When you eat a certain thing, or you feel a certain way, if it keeps going -- you know, get it checked out."

"Go see your doctor, run the tests, which is what I did for years...really be your own best advocate for your own health," he added.

Mathison stars in "The Christmas Club" on the Hallmark Channel which premieres Wednesday, Nov. 27.