Actor and comedian Dave Coulier came to his Full House costar John Stamos' defense amidst the backlash of Stamos donning a bald cap in solidarity with his cancer-ailing buddy.

Stamos was slammed with negative comments on a social media post featuring a photo of him with Coulier, who opened up about being diagnosed with stage 3 cancer in an interview with Hoda Kotb on the Today show last week.

Coulier was informed he had stage 3 non-Hodgkin lymphoma, a type of blood cancer that starts with the formation of malignant cells in the lymphatic system.

He detailed his cancer journey with optimism, saying his condition was "very treatable" after a bone marrow sample indicated that the cancer hadn't spread and his curability rate increased to above 90%.

Stamos, who played "Uncle" Jesse Katsopolis on the beloved family sitcom Full House and its spinoff series Fuller House, penned a heartfelt post to Coulier, who portrayed "Uncle" Joey Gladstone on the show.

The post featured a photo of Coulier, who lost his hair while undergoing a series of treatments, including chemotherapy, and Stamos in a bald cap to show Coulier had a support system in his friendship and to express he wasn't alone in his fight.

Stamos wrote in the caption:

"Nothing like throwing on a bald cap and flexing some Photoshop skills to show some love and solidarity with my bro @dcoulier."

He continued:

"You're handling this with so much strength and positivity -- it's inspiring. I know you're going to get through this, and I'm proud to stand with you every step of the way. I love you."

Stamos tagged and gave a shout-out to Coulier's wife, Melissa, calling her "the most wonderfulest" and Coulier's "true life line!"

While the post was generally received warmly, some people trolled Stamos for his partial act of solidarity in not shaving his head.

"Seriously just couldn't shave your head bro ?? lol," one person wrote.

Another accused Stamos of chasing clout, writing:

"What a shallow gesture! Couldn't even cut your hair off for your friend. And you made sure to post it on Instagram to get those likes too."

A third said:

"It'll grow back show some real love shave your head..."

Coulier responded to the negativity by explaining the special bond he shares with Stamos and that humor has always been a saving grace in difficult times.

He wrote:

"I'm sorry to see a bunch of negative comments as I've just begun my cancer journey."

"It's our friendship (me and John) and this is how we are handling a very tough time."

"I'm a comedian and humor is what drives me. John knows how to cheer me up and I laughed out loud when he arrived wearing a bald cap - being a true loving friend and brother."

Coulier also took his situation and turned it into a teachable moment to encourage people to stay up on their regular checkups to prevent serious illness, as early detection is key.

He continued:

"I have heard from so many people who have been inspired enough by my words and actions to say that they are going to check in with their doctors and get mammograms, a colonoscopy or a prostate exam."

"I'm still going to laugh in the face of adversity," wrote Coulier, and opened up about taking inspiration from family members who've struggled with cancer.

"When I lost my sister, Sharon, my mother, Arlen, and my neice, Shannon to cancer, we tried to stay positive, and we made each other laugh through the worst of it," he said, adding:

"So I'm choosing to spread the word about early cancer detection to help people."

Fans expressed support for Coulier and told him his explanation wasn't necessary.

Coulier shared his experience going through the first of six chemotherapy treatments, saying it has its ups and down.

"I have my good days. I have my bad days," he said.

"Some days are nauseous and dizzy, and then there's other days where the steroids kick in, and I feel like I have a ton of energy. I actually skated yesterday with some friends here in Detroit."

Coulier is expected to be in "full remission" by next February.