"Nothing like throwing on a bald cap and flexing some Photoshop skills to show some love and solidarity with my bro @dcoulier," Stamos said in the caption. "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."
'Full House' star Dave Coulier diagnosed with stage 3 cancer
In a "p.s." note, he continued by saying that Coulier's wife Melissa is "the most wonderfulest - your true life line!" Stamos played Jesse Katsopolis opposite Coulier's Joey Gladstone character on the fan-favorite sitcom "Full House," which lasted for eight seasons from 1987 to 1995. In the series, the duo lived in the San Francisco home of friend Danny Tanner, portrayed by the late Bob Saget, and helped parent his three daughters.
The star-studded cast's daughters included D.J., played by Candace Cameron Bure, Jodie Sweetin's character Stephanie and catapulted the careers of future fashion designers Mary-Kate and Ashley Olsen, who took turns starring as youngest daughter Michelle.
Coulier revealed Wednesday he was recently diagnosed with stage 3 Non-Hodgkin lymphoma, which he shared in an episode of his podcast "Full House Rewind" and in a People magazine story.
Stamos previously showed support for his former co-star in a touching Instagram post that included a gallery of photos of them over the years.
"My brother from day 1," he wrote. "Love you @dcoulier and I'll be by your side through it all."
Coulier told People magazine he was diagnosed in October after experiencing swelling in his lymph nodes due to an upper respiratory infection. "Three days later, my doctors called me back and they said, 'We wish we had better news for you, but you have non-Hodgkin's lymphoma and it's called B cell and it's very aggressive,'" he told the magazine.
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The actor added: "I went from, I got a little bit of a head cold to I have cancer, and it was pretty overwhelming. This has been a really fast roller coaster ride of a journey."
In the episode of "Full House Rewind," Coulier was wearing a hat, telling viewers he has begun chemotherapy and cut his hair as a "preemptive strike." He said he wanted to talk about his "personal battle" because "cancer has affected nearly all of us," noting he lost his sister, niece and mother to cancer. His older sister is also currently battling cancer.
He told Today.com that "I told Melissa I don't know why, but I (am) OK with whatever the news (is) going to be no matter how devastating. ... I can't explain where that came from," he told the site. "I've had an incredible life. I've had the most amazing people in my life."
"This has been an extraordinary journey, and I'm OK if this is the end of the journey," he continued.
He also told Today that he has underwent three surgeries so far and undergone one round of chemotherapy, with the next round scheduled for Friday. But doctors say Coulier should be done with chemotherapy and in "total remission" by February if all goes well, he said.
According to the Mayo Clinic, non-Hodgkin's lymphoma is a type of cancer that begins in the lymphatic system where "white blood cells called lymphocytes grow abnormally and can form growths (tumors) throughout the body." Signs and symptoms can include swollen lymph nodes, abdominal pain and chest pain.