It was the hospital Princess Diana chose for her first solo charity trip.
So it is rather fitting that the Duchess of Cambridge should follow suit for her second official engagement since the Royal Wedding with husband Prince William today.
Kate was all smiles in an elegant cream Amanda Wakeley dress at the Royal Marsden NHS Foundation Trust in South London, where she spent the afternoon meeting medical staff, young patients and their parents.
William, president of the Royal Marsden NHS Foundation Trust, poses with patient Ellis Andrews at the Royal Marsden NHS Foundation Trust in South London
The Royal couple also met Digby Davidson as part of their tour of the Oak Centre, a new £18m cancer unit
A sleep-deprived William, who flew a mercy mission just hours before opening the new £18 million children's cancer unit, looked slightly less sprightly but just as enthusiastic as he chatted with patients.
William and Kate, both 29, are touring the Oak Centre for Children and Young People which has been built to treat day and inpatients.
Before the couple's arrival, patients and hospital staff crowded on to the building's balconies, some waving Union flags, and a huge cheer erupted as Kate and William's car pulled up.
After waving to the crowds, the Duke and Duchess met Royal Marsden's chief executive, Cally Palmer, and chairman, Ian Molson.
Kate chats animatedly to 18-year-old patient Beth Ansell
Referring to his overnight search and rescue call-out, William joked: 'It was a bit of an early morning.
'It's great to be here finally - we've been talking about this for a while.'
The couple met two young leukaemia sufferers as they toured the new unit which has greatly improved the facilities for patients.
They joined Digby Davidson, 14, and his parents, Hermione, 41, and Fergus, 38, in a four-bed ward.
As the Duke walked in, he had his jacket off, sleeves rolled up and was rubbing antiseptic gel into hishands.
The Duke and Duchess of Cambridge were greeted by a huge cheer and fans carrying Union Jacks
The Duchess, wearing a Amanda Wakeley dress, is spending her time trying to get to know various charities and good causes so she can decide what her future role will be
Digby was treated for cancer last year but suffered a relapse which meant he had spent much of the previous three months in the new hospital unit which began treating patients in 2010.
William asked the teenager if they could join him on the bed and they laughed as the head of the bed was lowered and the royal couple sat either side of the young patient.
In a nearby bright lime green alcove containing a series of shelves, Digby had a few personal possessions and William quickly spotted a picture of the 14-year-old in military uniform.
'Is that you?' the Duke asked, and Digby, dressed in flip flops, bright Bermuda shorts and a dark T-shirt, explained he was in the Army Cadet Force.
Mrs Davidson made everyone laugh when she said her son had missed Army camp because of his relapse.
Welcome wagon: Kate greets some if her younger fans
Children and hospital staff wait for the couple to arrive carrying a welcome banner
The teenager and his parents spent around 10 minutes chatting privately to the royal couple and Mrs Davidson said afterwards: 'William was joking about Digby's flip flops and shorts - he said he had a tropical theme that fitted in with decor.'
Digby, the 14-year-old leukaemia patient, said later: 'William and Kate were asking when I last came in and if my friends came to see me.'
Mrs Davidson, a special needs teacher from Haywards Heath in West Sussex, said the royals came across as a normal couple.
She said: 'They were just very laid back and easy to talk to, it didn't feel strange.'
Later Harry Poil, 12, and his father Tony, 55, a Gatwick Airport security officer from Crawley, West Sussex met the Duke and Duchess.
Prince William, greeting hospital staff, was also invited to unveil a plaque to officially open the centre
The sleep-deprived Duke flew a mercy mission to take a sailor to see a seriously-ill relative just hours before today's even, left, while Kate looked as glossy as usual
The schoolboy said sport was the topic of conversation he shared with William.
The 12-year-old said: 'I'm a Chelsea supporter and we were chatting about last night's (Champions League) match. We had a penalty against us and William thought it was a bit dubious.
'He asked me if I was a cricket fan, and I said I was, and if I had been following the Ashes series. Kate said she was more into rugby than football.
During the visit, William was reunited with Alice Marples, a cancer patient who interviewed him two years ago for the CBBC Newsround programme.
The 12-year-old, who is due to fly to America to receive radiotherapy for a brain tumour, presented Kate with a bouquet of flowers when she arrived at the hospital.
Kate received a bouquet of flowers from Alice Marples, a cancer patient who interviewed Prince William two years ago
First solo trip: Diana visited the Royal Marsden in 1982
A St James's Palace spokesman told the London Evening Standard: 'The Duke is looking forward to seeing Alice again and finding out how she has been.
'Through his close connection with the hospital he has met many inspirational young people, like Alice, who have shown such bravery in battling their illness.
'Tomorrow, he is keen to show the Duchess the incredible work the Royal Marsden does to help Alice and others like her.'
William is president of the Royal Marsden - the first hospital in the world dedicated to cancer treatment and research into the causes of the disease.
He took over from his mother, who took on the role in 1989 until her death in 1997.
William went without sleep last night as he ferried the serviceman from a warship off the Isle of Man to Sandhurst in Surrey.
The royal flew back to his base at RAF Valley on Anglesey just after 9am before making the trip to open the Royal Marsden's new £18 million children's cancer unit in Sutton, south London, a few miles from Sandhurst.
The duke, an RAF search and rescue force helicopter co-pilot, carried out the 'compassionate call-out' during a normal 24-hour shift which also saw him help pick up a casualty with serious head injuries in Snowdonia.
The Royal Marsden is a cancer centre specialising in diagnosis, treatment, research and education
A St James's Palace spokesman said the duke would have got little, if any, sleep and was expected to arrive at Oak Centre for Children and Young People on a royal flight helicopter this afternoon.
His wife, who was in London, was arriving by car.
The royal couple have been enjoying married life together in North Wales since their glittering nuptials in April.
They have deliberately kept a low profile over recent months as the Duke, a flight lieutenant with the RAF Search and Rescue Force, is focusing on earning a promotion to captain.