By Marianne Garvey, CNN

(CNN) -- Lupita Nyong'o wrote a touching tribute to her "Black Panther" co-star Chadwick Boseman, saying the actor's death from colon cancer "doesn't make sense."

In her first public words following his death, Nyong'o wrote on Instagram: "I write these words from a place of hopelessness, to honor a man who had great hope. I am struggling to think and speak about my friend, Chadwick Boseman, in the past tense. It doesn't make sense. The news of his passing is a punch to my gut every morning."

She praised Boseman for always having the right energy, saying "I am aware that we are all mortal, but you come across some people in life that possess a immortal energy, that seem like they have existed before, that are exactly where they are supposed to always be - here! ... that seem ageless.... Chadwick was one of those people."

Nyong'o played Boseman's King T'Challa's love interest Nakia in "Black Panther," and while she says she didn't know her costar long, he will stay with her always.

"Chadwick was a man who made the most of his time, and somehow also managed to take his time," she wrote. "I didn't know him for long, but he had a profound effect on me in the time that I did. When we came together to make Black Panther, I remember being struck by his quiet, powerful presence. He had no airs about him, but there was a higher frequency that he seemed to operate from. You got the sense that he was fully present and also somehow fully aware of things in the distant future. As a result, I noticed that Chadwick never seemed rushed! He commanded his time with ease."

Nyong'o described Boseman as showing up to "every rehearsal and training and shoot day with his game face on."

"He was absorbent. Agile. He set the bar high by working with a generosity of spirit, creating an ego-free environment by sheer example, and he always had a warm gaze and a strong embrace to share. His large hands would descend on my shoulders and give them a squeeze that relieved me of the tensions I did not realize I was holding. Chadwick's hands were strong enough to carry the weight of the film and free enough to clasp mine when I needed it."

Ultimately, she wrote, "it seems that it was life that gave up on Chadwick long before Chadwick gave up on life,"

Nyong'o on Tuesday posted a photo of her and a laughing Boseman to Instagram.