Wentworth Miller revealed he was diagnosed with autism a year ago. 

The 49-year-old "Prison Break" actor said the diagnosis was a "shock," but that he wasn't surprised.

"This fall marks 1 year since I received my informal autism diagnosis," Miller wrote in the caption of an Instagram post on Sunday. "Preceded by a self-diagnosis. Followed by a formal diagnosis."

"It was a long, flawed process in need of updating. IMO," he added. "I'm a middle-aged man. Not a 5-year-old. And (it's a "both/and") I recognize access to a diagnosis is a privilege many do not enjoy. Let's just say it was a shock. But not a surprise."

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Wentworth Miller attends a movie premiere in Tokyo, Japan.

Wentworth Miller revealed he was formally diagnosed with autism last fall. The 49-year-old actor shared the news on his Instagram account. (Photo by Jun Sato/WireImage via Getty Images)

Miller also noted that he doesn't "know enough about autism." "(There's a lot to know.) Right now my work looks like evolving my understanding. Re-examining 5 decades of lived experience thru a new lens," he wrote.

"That will take time," he stated. "Meanwhile, I don't want to run the risk of suddenly being a loud, ill-informed voice in the room. The #autistic community (this I do know) has historically been talked over. Spoken for. I don't wish to do additional harm. Only to raise my hand, say, "I am here. Have been (w/o realizing it)."

Miller went on to say he wouldn't "change" his autism diagnosis as it's "central" to who he is.

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"Oh - this isn't something I'd change," Miller wrote. "No. I get - got - immediately being autistic is central to who I am. To everything I've achieved/articulated."

"Oh - I also want to say to the many (many) people who consciously or unconsciously gave me that extra bit of grace + space over the years, allowed me to move thru the world in a way that made sense to me whether or not it made sense to them... thank you," he added. 

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"And to those who made a different choice... well. People will reveal themselves," the star shared. "Another gift."

Miller became well-known after he starred as Michael Scofield in the FOX series "Prison Break."