Stevenson, of the Hamilton Argyll and Sutherland Highlanders, made the statement through the federal government’s Department of National Defence on Monday.
He said Cirillo was “more like a brother” than a friend. The two had met in Grade 9.
“We were pretty much inseparable,” Stevenson said. “He was the first from our group of friends to join the Canadian Armed Forces and it earned him the nickname Army Nate.”
Cirillo died on Oct. 22 after he was shot by Michael Zehaf-Bibeau that morning. The assailant was shot by law enforcement officials in the halls of Parliament a short time later, after storming the building with a rifle.
According to a statement from the RCMP, Cirillo and Stevenson were standing guard at the Tomb of the Unknown Soldier when the gunman ran at the duo on angle that would have made him difficult for them to see.
Zehaf-Bibeau reportedly fired at Cirillo twice, wounding the soldier before he later died. He shot at Stevenson but missed and ran away from the monument.
Stevenson then pursued the gunman, but turned back to tend to Cirillo.
Ron Foxcroft, the honorary colonel of the Argyll and Sutherland Highlanders of Canada regiment, has commended Stevenson for his actions and “tremendous bravery.”
Last week, RCMP Commissioner Bob Paulson told the media that a video featuring Zehaf-Bibeau that was made in the lead-up to the attack suggests he was driven by political and ideological motives.
Paulson said the video was broadly related to Canadian foreign policy, and in it, the gunman makes reference to "Allah."
My heart goes out to his family
In his Monday statement, Stevenson said the attack “left me in shock and grieving the loss of my best friend.
“My heart goes out to his family for the terrible loss they have to endure. I am still struggling to cope with everything that has happened.”
Here’s the full text of the statement:
"Nathan Cirillo was my friend, though he was more like a brother. We met in Grade 9 and from that time on, we were pretty much inseparable. He was the first from our group of friends to join the Canadian Armed Forces and it earned him the nickname 'Army Nate.' It was his love of the Army that inspired me to join, and I remember going to his house to practice my swearing-in ceremony.
"We did everything together from hanging at the mall to going on double dates, so it was an incredible honour when we were both chosen to come to the National War Memorial to stand-to as sentries. We were very proud to be here together watching over the Tomb of the Unknown Soldier, honouring all those who have fallen.
"Over the past few years, Nathan and I would routinely drive around together, making jokes that no one else would understand. Neither of us had much of a voice, but that didn't stop us from singing along with every song on the radio, whether we knew the words or not. It seemed as if we were always laughing and joking about something. The morning of October 22 was no different. As we stood sentry and walked the beat, one of my socks was sagging. Nathan smiled and intentionally kept our walk going so my sock would fall a little more. He had such an amazing personality!
"What happened shortly after left me in shock and grieving the loss of my best friend. My heart goes out to his family for the terrible loss they have to endure. I am still struggling to cope with everything that has happened. My family, the Argyll and Sutherland Highlanders in Hamilton, and my extended family within the Canadian Armed Forces are helping me through this very difficult time. I am overwhelmed by the outpouring of support from across Canada and around the world.
"In the coming days, I'll be resuming my duties at the National War Memorial. It will not be an easy task, but I am resolved to do it in honour of Nathan, Warrant Officer Patrice Vincent, and all those who stood, and continue to stand, on guard for Canada. I still believe Canada is a nation of peace where soldiers within its borders need not take up arms. My fellow soldiers and I remain proud and committed to watching over the Tomb of the Unknown Soldier as a strong, silent reminder of every person who made the ultimate sacrifice.
"I now have to learn to live without someone who was closer to me than I can put into words. When I resume my post, I will not be conducting interviews with media. I appreciate, in advance, your consideration and respect for my privacy during this difficult time.
"Nathan Cirillo was my friend, my best friend, my brother. I will miss him forever."