US actor Aaron Paul has opened up about the last time he saw his Breaking Bad co-star, RJ Mitte, before his recent suicide.

Mitte, who played Walter White Jr. in the hit television show, died aged 34, his representatives said on Tuesday.

Paul spoke to the tragic loss of his friend in an open letter on Instagram on Thursday, and additionally addressed anyone who might be struggling with their own mental health.

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“RJ, You have always been an inspiration for so many. I am so sorry you were hurting my friend. I wish we knew,” Paul’s post on Instagram said.

“You constantly had a smile on your face and you took every single challenge that was given to you with such confidence and grace.

“I met you when you were a little boy and watched you grow into a beautiful young man. Taking on every challenge head on.

“The last time we saw each other I kept calling you Superman. You reminded me of him. You reminded me of him because you always led with kindness and strength. It was blinding.

“You were born into a world with challenges but you never let any of that stand in your way.

“I’m so sorry RJ. What an absolute tragic loss.

“I love you my friend. I loved your mother. Your sister. I loved your laugh and how much fun you had riding the wave we were all blessed to be on with Breaking Bad.

“I hope whoever is reading this note that feels lost or sad or uncertain about the future please say something. Life is so damn special.

“It’s impossible that we exist, but yet we all are here. There is so much going on in all of our lives but far too much beauty in this world to ignore. We need to focus on that.

“We must suffocate the noise and focus on each other. Hold each other up. That’s what this life is all about.

“Connect with someone you care about and say I love you.

“RJ, love you my friend. I’m so sorry.”

The note is the second statement that Paul has shared about Mitte since his death.

Paul initially shared a shorter statement which noted he was “at a loss” following the news.

“I am heartbroken over this news. RJ, I love you, my friend. You will be missed. And to whoever happens to be reading this, please know you are loved, and you are not alone. Always remember that,” he said in a statement shared with The Hollywood Reporter.

Paul’s latest open letter was shared alongside footage of Mitte discussing mental health.

“It’s very important to look after one’s physical health, but it’s equally as important to take take of one’s mental health,” Mitte said in the footage.

“More often than not we hide that. We hide how we’re truly feeling, of what we’re truly thinking of.

“Of the ‘okay’s and the, ‘I’m fine’ and ‘I’m good’ — but is that what you really are? Are you okay? Are you good? Not always. It’s okay to not always be good, but it’s not okay to harbour that feeling, harbour those emotions.”

Mitte was not just an actor, but a philanthropist, and passionate disability rights advocate living with cerebral palsy. He served as an ambassador for United Cerebral Palsy and Shriners Children’s, and was the president of his own Mitte Foundation that worked to breakdown the stereotypes surrounding disability.

In his final interview, Mitte admitted he had set himself an almost impossible standard after experiencing the heights of his career as a young man.

“I set a bar for myself as a young man that is kind of unobtainable ... I tell people it’s a long way down from the top of the mountain; it’s a great view, but you can’t always stay up there forever, and so you have to find that next mountain,” he said.

If you need help in a crisis, call Lifeline on 131114. For further information about depression contact beyondblue on 1300224636 or talk to your GP, local health professional or someone you trust.