— The death of Eugene Cernan, the last man to walk on the moon, elicited heartfelt remembrances from his fellow astronauts and those now working at NASA to follow in his footsteps.

"As commander of our December 1972 Apollo 17 mission, he was an outstanding crewmate," wrote Harrison Schmitt, who with Cernan were the last moonwalkers to explore the lunar surface. "Geno, I wish you had time for one more run in the [Lunar Module Simulator] before you leave. Have a good flight. Again, God Speed..."

Cernan, who died Monday (Jan. 16) at age 82, launched three times to space and was one of only three astronauts who flew to the moon twice. In addition to leading the final moon landing, Cernan became only the second American to walk in space during the Gemini 9 mission in 1966, and was lunar module pilot on Apollo 10, the "dress rehearsal" for the first moon landing, in 1969.

"I've lost the brother I never had," stated Thomas Stafford, who led both Gemini 9 and Apollo 10. "We flew together twice. We lived through several life and death experiences in those missions."

"I will never forget our great friendship and [the] trust we developed for one another. We were a great team, and he will be greatly missed," said Stafford in a statement shared by the Oklahoma museum that bears his name.

With Cernan's death, six out of the 12 humans who walked on the moon are now deceased.

"I lost another friend and the world lost another hero," said Apollo 11 lunar module pilot Buzz Aldrin.

"With the passing of the First Man — Neil Armstrong, and the passing of the Last Man — Gene Cernan, it is up to us 'Middle Men' to carry on spirit of Apollo into the future for our nation and the world," Aldrin wrote on his website.

Cernan was a strong advocate for expanding U.S. human space exploration beyond Earth orbit, joining fellow Apollo astronauts Jim Lovell and the late Armstrong in delivering testimony before Congress to support returning astronauts to the moon. Although Cernan titled his memoir "The Last Man on the Moon," it was not a distinction he desired.

"Very sad to see that the world has lost Gene Cernan. The last man on the moon, but he didn't want to be," tweeted Tim Kopra, who commanded the 47th expedition on board the International Space Station in 2016.

"America has lost a patriot and pioneer who helped shape our country's bold ambitions to do things that humankind had never before achieved," said Charles Bolden, NASA Administrator and former space shuttle astronaut. "Gene's footprints remain on the moon, and his achievements are imprinted in our hearts and memories."

"He was one of a kind and all of us in the NASA family will miss him greatly," Bolden said in a statement.

In addition to his fellow astronauts, tributes were shared by many of the organizations Cernan worked with, including the San Diego Air and Space Museum in California, Space Center Houston, the Coalition for Deep Space Exploration and the Astronaut Scholarship Foundation.

"Gene Cernan will always be remembered as the 'last man on the Moon' — at least until the next person walks there," Michael Neufeld, a curator in the space history division at the National Air and Space Museum in Washington, D.C., wrote on the Smithsonian museum's website. "Perhaps the most articulate of the moon-walking astronauts, he felt that it was his mission to make his audiences feel as if they had been there too."

Cernan is survived by his second wife, Jan, his daughter and son-in-law, Tracy Cernan Woolie and Marion Woolie, step-daughters Kelly Nanna Taff and husband Michael and Danielle Nanna Ellis and nine grandchildren.

"We truly appreciate everyone's thoughts and prayers," the Cernan family said in a statement released on Monday by NASA. "Gene, as he was known by so many, was a loving husband, father, grandfather, brother and friend."

"As we say goodbye, it seems fitting to share the last line in Gene's book, as he explains his experience of walking on the moon to his then five-year-old granddaughter, 'Your Poppie went to Heaven. He really did.'"