Watch: Wentworth Miller discusses his autism diagnosis
The Prison Break star said it came as a "shock but not a surprise", adding that the diagnosis had been a long, flawed process that he felt needed updating.
Miller, 49, revealed in a lengthy Instagram post: "Like everyone, life in quarantine took things from me. But in the quiet/isolation, I found unexpected gifts.
"This fall marks one year since I received my informal autism diagnosis. Preceded by a self-diagnosis. Followed by a formal diagnosis.
"It was a long, flawed process in need of updating. IMO [In my opinion]. I'm a middle-aged man. Not a five-year-old. I recognise access to a diagnosis is a privilege many do not enjoy.
"Let's just say it was a shock. But not a surprise."
The Legends Of Tomorrow actor said he was not ready to become a public spokesman about autism.
He said: "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.'"
But Miller said he needed to re-examine the past five decades of his life "through a new lens", adding, "I get – got – immediately being autistic is central to who I am. To everything I've achieved/articulated."
And the actor – who has previously spoken about battling depression since childhood – thanked those who had been supportive of him in the past.
He said: "I also want to say to the many people who consciously or unconsciously gave me that extra bit of grace and space over the years, allowed me to move through the world in a way that made sense to me whether or not it made sense to them... thank you."
He added: "And to those who made a different choice... well. People will reveal themselves."
Autism is a developmental disorder which can affect social interaction and communication to varying degrees.
Miller rose to fame playing Michael Scofield in hit Fox drama Prison Break from 2005 to 2009.
The actor was born in Oxfordshire to American parents and grew up in Brooklyn. He holds duel UK and US citizenship.
He came out as gay in 2013 having previously publicly denied his sexuality.
Miller later revealed he had attempted suicide multiple times a teenager.
If you are in need of emotional support you can call the Samaritans 24-hour helpline on 116 123, email firstname.lastname@example.org, visit a Samaritans branch in person or go to the Samaritans website, www.samaritans.org.
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