Simon Kennedy is certain that his mum Yvonne would have been doing all she could to comfort her fellow passengers on Flight 77, on its way from Washington to LA.
"She would have been holding someone's hand or doing something to help on the plane as it went down," he tells Woman's Day.
"She was always helping people. That was her life."
Yvonne Kennedy was 62 and on the trip of a lifetime to Canada and the US when she died on the American Airlines flight hijacked by terrorists on September 11, 2001, and crashed into the Pentagon.
Having recently retired from a 25-year long career with the Red Cross, adventurous Yvonne, who hailed from western Sydney, was set to travel to LA and Hawaii before heading home a few days later.
"I used to think that being an Australian 9/11 family member was such an unusual thing, being there were only 10," says Simon.
"But just because we don't salute the Stars and Stripes, doesn't mean we didn't go through the same pain."
And losing his beloved mum in such a terrible way is a pain Simon has worn for two decades.
But Yvonne's big personality has ensured she remains vivid in his memories.
"She was incredible," is Simon's answer when asked to describe his mum.
"She was strong and she was brave and she was quite funny – and she would have told you that!"
Yvonne also made her mark on others.
"We got letters from people on her tour group after the events of 9/11, talking about how wonderful and what great company she was. She was loved by everyone."
Yvonne raised Simon and his brother on her own after being widowed at a young age.
"She'd lost the love of her life and she managed to do a great job," says Simon, now a comedian, broadcaster and keynote speaker on resilience.
"She went back to work and threw herself into the Red Cross."
"She was there when the Granville train disaster happened, she was there helping out with the Thredbo landslide.
"She was hands-on and put herself in harm's way to look after people."
Simon, now 46, was in his 20s when he received the phone call late in the night, Australian time, and learned what had happened thousands of kilometres away in the US.
"That phone call made me pick up the itinerary she had handed me the day she left.
"It didn't take long to start putting the pieces together and work out that Flight 77 was the one that had gone down."
No confirmation came from official channels for weeks, however Simon and his now-wife Tahnee called the airline and every hotel Yvonne had stayed in or was set to visit, just in case she hadn't got the flight.
"It was quite a false hope we had... I knew logically, pretty quickly.
"But I left the door open, hoping," he says.
A memorial service for Yvonne was held at Sydney's St Mary's Cathedral eight days after her death, with more than 1000 people in attendance.
She is one of two Australians with remains buried in Washington DC's Arlington Cemetery.
Over the years, Simon has attended 9/11 memorial services in the US and met President Barack Obama.
This year he planned to take his family to New York for the occasion, but the pandemic forced a change of plans.
But whether at home in Sydney or overseas, remembering Yvonne on the anniversary of her death always comforts Simon and helps with his loss.
"I think it helps – it makes me take stock. I feel proud of what I've weathered and who I am, that I've gone through it all and I'm not a big ball of rage and hate.
"That I am not perfect but that I've managed to find gratitude in the beautiful life that I do have."
That life includes Simon's two children, Adelaide, 14, and Fletcher, 11, who have heard all about their incredible grandmother.
"One good thing about missing someone is you tend to talk about how much you care for them and how wonderful they were, so Mum's not forgotten and she's spoken about," says Simon.
"But the place at the table that she doesn't occupy at events is certainly noted. She was so loved within the wider family and she is missed."
Simon's book, 9/11 And The Art Of Happiness, is available on Amazon or on his website.