It is believed that William, who has been president of the charity since 2007, will be hosting the event without his wife the Duchess of Cambridge, née Kate Middleton, although royal watchers are hoping that she will make a surprise appearance.
According to reports, 74-year-old Ralph is making a two-day trip to the UK specifically to attend Prince William's event.
William followed in the footsteps of his mother Diana, Princess of Wales, in becoming president of the Royal Marsden Cancer Charity.
Since taking on the role he has launched fundraising projects, helped look after patients and has undertaken numerous hospital visits to show his support.
Ralph Lauren is expected at Prince William's charity dinner
In September 2011 William and Kate opened a new £18 million children's cancer unit at the Royal Marsden Hospital in Surrey, spending hours touring the Oak Centre Unit and meeting the youngsters being treated there.
The Sutton hospital holds a special place in William's heart and it was an engagement he was determined not to miss — flying straight to the hospital after finishing one of his RAF shifts.
Prince William and the Duchess of Cambridge at the Royal Marsden in 2011
William's late mother Diana was a huge supporter of the hospital and auctioned off 79 dresses to help raise funds for the charity weeks before her passing in 1997.
A decade later the hospital was one of the charities to benefit from Concert for Diana, a celebratory event staged by her sons.
In 2008, royal help was needed once again when a fire broke out in one of the wings, leading to the evacuation of those being treated. William came in person to thank firefighters and lift spirits among nurses and patients, following this up with another visit to check on repair work.