"It is a very important issue to our family. We have my sister because of organ donation," she said through tears.
"Nearly six years [ago], and she's about to have another baby. Just something none of us thought would happen... She's a gorgeous mum," she added.
Allison's co-host Karl Stefanovic tried to lighten the mood by asking her, "Is she a real troublemaker your sister?"
"She's a big trouble maker, yeah,” Allison responded jokingly.
“I mean, I'm the angelic one... She's always been a problem."
Grabbing himself a tissue, Karl said, "Now I'm crying, because I just know that's just not true."
On a serious note, he added, "You're a beautiful woman, Ali. And that is such a lovely thing to share with everyone and it's such an important message at this time, because it's something you need to sit down with your family and to plan out. Because we've seen life that comes from those worst possible circumstances, your sister included."
"Yeah, it's such a gift to give that and it is Donate Life Week," Allison replied, adding that viewers could learn more at the Donate Life website.
In an interview with Mamamia, Allison shared her sister Kristen's story, revealing that when she was just 11 she was diagnosed with diabetes.
In 2010, after Kristen gave birth to her first baby, a daughter, who arrived 13 weeks early, Kristen's health began to worsen.
"The first four years of [my daughter's] life, she did not have a healthy mum,” Kristen said.
“I was constantly exhausted as my body struggled with the buildup of toxins that my failing kidneys couldn’t process.
“For years, that was my life until the decision was made in early 2014 that I needed dialysis."
Allison said it broke her heart to see her sister constantly hooked up to machines.
"She couldn't run around and do all things that she wanted to do with her little girl... She's such a beautiful mum. She's the most extraordinary mum, with just so much love to give."
A suitable kidney and pancreas donor was thankfully found in 2014.
"That moment was surreal,” Kristen said.
“I immediately called my husband and parents, and we were at Westmead Hospital within two hours.
“It was possibly the longest day of my life... I felt elated that I was getting my long-awaited transplant, but also an overwhelming sense of guilt for the loss another family was suffering. It was a lot to deal with."
"At 7pm that night, I was wheeled in for surgery. I kissed my husband and parents and told them to look after my precious little girl if things went wrong. I was scared."
Within a week, Kristen showed signs that the transplant was successful and doctors were very happy with her progress.
"My transplant has given me a second chance at life,” she added.
“My daughter is almost ten now and having a sick mum is, luckily, a distant memory for her."
"I truly don't know how you sum up the gift that this person and their family gave to my sister and to us," Allison said.
"Giving the gift of life, how do you get your head around that?
“We also knew that in that moment, when my sister was given an opportunity to live a normal life, that another family somewhere was experiencing the worst day imaginable. And we were so very much aware of that."
Kristen agreed, saying she still feels conflicting emotions on her transplant anniversary. She added she has a huge amount of respect and gratitude for her donor's family.
The sisters stressed the importance of people having conversations with their family about organ donations so that if the situation should arise, your loved ones know your wishes.
However, you can make your wishes clear by going online and signing up to the Australian Organ Donor Register.
"My donor's choice gave my family back a wife, mum, sister, aunt, granddaughter, cousin and a friend,” Kristen added.
“It also gave me back my life."