Michael Collins, the pilot of Apollo 11, passed away at the age of 90.

Michael Collins, the pilot of the Apollo 11 control module and the first astronaut to orbit the far side of the moon alone, died at the age of 90 of cancer.

"Today, the nation has lost a true pioneer and longtime advocate of exploration in astronaut Michael Collins," NASA Administrator Steve Jurczyk said in a statement released Wednesday (April 28). "As pilot of the Apollo 11 command module — some called him 'the loneliest man in history' — while his colleagues walked on the moon for the first time, he helped our nation achieve a definite milestone."

During this famous mission, Collins worked alone in the command module "Columbia" for 21.5 hours, during which time the module drifted behind the moon, reported earlier Space.com. In the final moments, before he temporarily lost touch with Mission Control, he wrote: I am alone now, really alone, and absolutely isolated from all known life. I am it. If we did a tally, it would be $3 billion-plus two on the other side of the moon, plus God knows what on that side.”

Hence, Collins earned the nickname "loneliest man in history;" he's also been called the "forgotten astronaut," since he was on the Apollo 11 mission but never walked on the moon as Neil Armstrong and Buzz Aldrin did that day, NPR reported.

"It's a shame that when people are asked, 'Can you name the Apollo 11 crew.' Mike Collins is normally the name that doesn't come to mind," Francis French of the San Diego Air and Space Museum and author of many books on the space program, told NPR. "He was the one who really knew how to fly the spacecraft solo (the only person who flew a spacecraft solo in the entire mission) and the only one who could get all three of them home."

In later interviews about the mission, Collins said he didn't really feel alone passing behind the moon, reports Space.com.

Behind the moon, it was very peaceful — no one at Mission Control speaks to me and wants me to do this, that, and the other. I was very happy, it was a happy home,” he said at an event organized by the Explorer's Club in 2019. That said, during the visit, Collins was concerned about the small colony of white mice they had brought to the mission, he admitted. The crew would quarantine themselves with the mice on their return to Earth, to see if the rodents had developed strange diseases during the voyage.

Before his second and final spacewalk on Apollo 11, Collins served as a pilot on Gemini 10, the 16th manned spacecraft to encircle Earth, according to Space.com. He has also played important roles with Mission Control on other missions, communicating with astronauts on board Apollo 8, for example.

After clocking more than 266 hours in space, Collins left NASA in 1970 and became director of the National Air & Space Museum in Washington, D.C., where he worked for eight years.

Regarding Collins' death, his family said "He spent his last days in peace, with his family beside him," according to NASA's statement. "Please join us in fondly and joyfully remembering his sharp wit, his quiet sense of purpose, and his wise perspective, gained both from looking back at Earth from the vantage of space and gazing across calm waters from the deck of his fishing boat," they wrote.

Original publication on Live Science.