"The best way we could explain [the diagnosis] was: 'You know Christian Lealiifano when he had to stop playing because he had leukaemia. Well, that's what you've got," mum Lisa said.

"He said: 'oh well, if he can beat it, I can beat it'. It was that amazing, positive reinforcement."

When the Brumbies run out for their first Super Rugby grand final in almost a decade, two Christians will be cheering them on.

Christian Lealiifano - the inspirational former captain who retired from the Brumbies last year after more than 150 games for the club. And Christian Franklin - the 10-year-old superfan who battled leukaemia this year and who will sit on the sidelines as the team's 24th man for the showdown against the Queensland Reds.

"I want a high-five from Christian Lealiifano," Christian beamed, even though his hero won't be on the field.

Lealiifano was diagnosed with leukaemia in 2016, shocking the rugby world and putting his career on hold. Doctors told him he would never play again, but he was back on the field in 2017 and led the Brumbies to a semi-final last year.

Inspiration will be easy to find for the Brumbies with the two Christians packed in among the 6000-strong crowd. It will be the biggest crowd in the ACT in more than six months after ACT Chief Health Officer Dr Kerryn Coleman allowed attendance to be increased for the game. Tickets for the grand final sold out within a few hours of going on sale to the general public.

But Christian and his parents, Lisa and Don, didn't need to nab tickets as they will be sitting with the Brumbies inner sanctum.

Christian has been battling leukaemia this year after he was diagnosed two days before Christmas.

When the team heard of Christian's story in March, they organised a special day for the family at their match against the Japan Sunwolves in Wollongong. At the time, Christian was undergoing treatment at the Sydney Children's Hospital. Lisa messaged the club about wheelchair access and received an overwhelming response.

Not only were they given sideline seats but they also got to meet the team and Christian even got to join in the team's victory song.

Since then, Christian finished treatment and is on maintenance, he will be on medication until Christmas next year. He recently started back at school.

"He was super excited to see all of his friends again," Lisa said. "He is very much normal back to the way he was ... super energetic, super crazy at times. His hair has started to grow back so he is really happy about that."

When Lisa and Christian were asked who they had tipped to win, there was no hesitation.

"They are going to win and I can't say it any other way than that," Lisa said.

Canberra will hop on the Brumbies bandwagon as landmarks are set to light up in blue and yellow this week.

Black Mountain Tower, Malcolm Fraser Bridge and the Light Rail will light up in the Brumbies colours every night until Saturday. Captain Cook Memorial Jet will be lit on Friday and the Ian Potter Foundation Technology Learning Centre on Friday and Saturday evenings.