By Katie Atkinson
July 31, 2013 at 11:50 PM EDT
David Livingston/Getty Images

Nick Cannon and Amanda Bynes both found fame on Nickelodeon’s All That, but their careers have taken drastically different turns since, with Cannon hosting America’s Got Talent and marrying superstar singer Mariah Carey and Bynes retiring from acting and lashing out with a series of arrests and bizarre tweets.

But Cannon hasn’t forgotten about his former castmate, and he’s often asked about her in interviews, given her recent involuntary psychiatric hold following one of those arrests. He posted an open letter to his “sister” online Wednesday, trying to explain to the public the pressures child stars face and how Bynes’ behavior might look “crazy” to some but makes total sense to him.

“Lately I have been hit with an onslaught of questions about someone I consider family, someone I watched grow up, and someone I genuinely feel is one of the most pleasant human beings I have had the pleasure of meeting, Amanda Bynes,” Cannon wrote. “The questions have ranged from, ‘Have you spoken to Amanda’ to ‘Are you working on her rap album.’ Sometimes I would answer in a playful humorous manner and sometimes I would brush it off as another pop culture topic that a reporter was trying to retrieve a sound bite for. But after recent events of Amanda being admitted under psychiatric care and reported as 5150, I see this as no laughing matter.”

While Cannon calls a career in entertainment “one of the best and easiest occupations to ever have,” he says “one must know how to navigate through the matrix or you may find yourself in a very dark hole.”

Before wrapping up his letter with some lyrics from Bill Withers’ “Lean on Me,” he addresses Bynes and offers help to his onetime co-star: So I say to my sister Amanda Bynes you’re not alone. I’m here for you. I understand. I care and I appreciate you, because that’s what family does and that’s what family is for.”