"You hope these things go forever, but everyone's got their own reasons," Luke, who played Ashley Stubbs in the series, told ET. "I'm very thankful for my part in that series and that journey was a big part of my life, but yeah it was disappointing."
Making it even worse for Luke was the fact that he got the cancelation news on his 42nd birthday. "I was like, 'F**k! Dammit!'"
As for fans who may be feeling similarly due to what some are calling an unsatisfying ending to the series, Luke acknowledged their frustrations but urged them to not focus on the negatives.
"I think the idea right from the start was to go full circle and come back to be about loops, to be about human beings and robots being stuck in that trajectory," he said. "Unfortunately, we get cut off, but it's the nature of the world. You can't get depressed about it. You move on and it opens up new doors."
Though Luke is bummed about Westworld's fate, he was excited to be on hand to support Chris at the Limitless premiere. The Disney+ docuseries, which features Chris taking on physical challenges, was an idea Luke loved the first time he heard about it.
"I said, 'I wish it was me,'" Luke recalled to ET of when Chris told him about the project. "It's cool you get to do all these tests and figure yourself against the best of the best. Chris crushes it."
While Chris remained the star of the show, Luke and their other brother, Liam Hemsworth, did make an appearance. Luke joked that he and Liam "for sure" hurt Chris rather than help him when they arrived to watch him dive into near-freezing Arctic waters.
"We were not there to help. We're brothers," he quipped. "You gotta fight a little to succeed, so we never ever let him know that he's succeeding, which makes him push a little bit harder."
Joking aside, Luke said he's "so proud" of his younger brother, noting of Chris, "Everything in that episode is like, 'Wow, he really is that specimen of a human.'"