The royal ladies, who are honorary patrons of the charity, helped to open a new blood cancer ward at University College London Hospital last week.
Beatrice and her mum Sarah were seen wiping away tears as Dr Adrian Whiteson OBE and Myrna Whiteson MBE, founders and life presidents of the charity, thanked the Duchess for her dedication and support for the past 32 years.
WATCH: Princesses Beatrice and Eugenie and mum Sarah Ferguson get teary on call with Teenage Cancer Trust
"Eugenie, Beatrice, you must be very proud of Mum because she has such humility and such empathy with patients," Dr Adrian said, as Eugenie, who was seated next to her mum, leaned over to give her a big hug.
Beatrice, who was dialling in from a separate location, was seen wiping away a tear as she smiled at the camera, while Sarah told the charity founders: "Well, we're very proud of you."
The Duchess became emotional on the video call
Myrna continued, "I just wonder when we enlist the little ones?" referring to Beatrice's daughter Sienna, who turns one in September, and Eugenie's son August, who celebrated his first birthday in February. "Give them a year or two and they'll be doing Teenage Cancer Trust."
"Sienna's already a lifelong patron," Beatrice said, smiling widely.
The Princess also recalled visiting a Teenage Cancer Trust ward on her 18th birthday and the impact it had on her future work. "My 18th birthday, I got to come down to the ward and meet some of the young people," said Beatrice. "And I think when you're a young person yourself, it changed for me the trajectory of, you know, what it is to be in service."
Beatrice admitted her daughter Sienna is already a "lifelong patron" of the charity
The call ended by the Duchess officially opening the new UCLH haematology ward to rounds of applause and cheers from participants on the call.
Prince Andrew's ex-wife has supported Teenage Cancer Trust since its inception. In a statement, she said: "This is a special charity that's so very close to my heart. Cancer doesn't just devastate a young person's health. It threatens to take away everything they care about – their identity, their independence, and their dreams.
The royals officially opened the new UCLH haematology ward
"Teenage Cancer Trust's specialist nurses and youth workers provide the very best care and support during treatment and beyond, making sure that cancer doesn't stop young people living their lives.
"I opened the first Teenage Cancer Trust unit for young people in London in 1990, and 32 years later, to be here with my daughters, helping to open this new blood cancer ward at UCLH, is truly remarkable. We are all honoured to be a part of this incredible charity."
Teenage Cancer Trust worked with Morgan Stanley employees to raise and donate over £600,000 of funding for the much-needed new ward that brings teens and young people with blood cancer together to be treated by experts in a place specially designed for them.
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