John Stamos supports Dave Coulier after he reveals cancer diagnosis

John Stamos is showing some brotherly love to his Full House costar Dave Coulier.

Dave Coulier and John Stamos in 2017.

 Kelly Lee Barrett/Getty

After Coulier revealed today that he’s been diagnosed with a “very aggressive” form of cancer, Stamos took to Instagram to make a public declaration of his devotion to his friend. “My brother from day 1. Love you [Dave Coulier] and I’ll be by your side through it all,” he wrote over a series of nine images of the men over the years.

Tellingly, the majority of the photos Stamos included were not from the Full House, a heartening demonstration that their bond is just as real off screen as it was on the beloved family sitcom.

Coulier detailed the diagnosis and current treatment process in an interview with PEOPLE. He first dismissed swelling in his lymph nodes to be complications from an upper respiratory infection he battled in October. When that swelling proceeded to grow to the size of a golf ball, he visited the doctor.

“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 said. “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.”

Stamos and Coulier starred alongside each other on Full House for nine years. As Jesse Katsopolis and Joey Gladstone, the half-brother and childhood best friend of Tanner family patriarch Danny (Bob Saget), they added an element of macho cool and dependable comfort that struck the perfect balance in the Tanner dynamic.

Much of the cast has remained close since, especially following Saget’s death in 2022. Stamos celebrated Coulier’s 64th birthday on Instagram last September, calling him “a gift in my life” and promising to “love you always.”

Melissa Bring, Coulier’s wife, commented on Stamos’ heartfelt post today, writing, “Love you PP – thank you for the daily support and love!!”

Coulier noted to PEOPLE that Bring has been instrumental in his treatment process. He said that she and an assortment of friends “all kind of put our heads together and said, ‘Okay, where are we going?’ And they had a very specific plan for how they were going to treat this.” When a bone marrow test came back negative for cancer, he reflected, “my chances of curable went from something low to 90 percent range…so that was a great day.”

Another point of hope for Coulier is the child his own son Luc has on the way. The baby, due in March, will make Coulier a grandfather for the first time. Coulier is expected to finish chemo a month after Luc’s wife Alex’s due date, prompting him to reflect, “There’s a lot to look forward to.”