Prince William's mother's long legacy has given the royal a whopping 30th birthday gift - nearly $20 million.
William stands to inherit the money under the terms of Princess Diana's will.
The precise amount has not been made public, but Diana's estate is thought to have grown substantially since her death 15 years ago.
Palace officials declined to comment on William's private finances, and it is possible he may choose to leave the money in a trust.
They said William, who turned 30 yesterday, marked the milestone in private with his wife, Kate Middleton, and some close friends. They said a low key celebration was planned.
Two reports said Kate planned to present William with a series of special gifts, including a scrapbook full of memories of their relationship, and a playlist full of music special to them.
The Daily Telegraph reported that Prince Charles had commissioned the artist Nicky Philipps to paint Middleton. It was thought he was planning to give the portrait to William as a birthday present.
Philipps previously painted the only joint portrait of Princes William and Harry.
William has been pursuing a military career as a search-and-rescue helicopter pilot while easing into married life and taking on more royal duties.
He is stationed at an air base in north Wales and was recently on a temporary deployment in the Falkland Islands in the south Atlantic.
He and Middleton have made a number of public appearances in recent weeks, often representing his grandmother, Queen Elizabeth II, at events to mark her 60 years on the throne, a year-long celebration called the Diamond Jubilee.
He has seemed increasingly comfortable in public, escorting Middleton, formally known as the Duchess of Cambridge, to high society soirees and "meet and greet" events.
There has been widespread speculation about the couple starting a family. The talk has been fueled by William indicating that he would like to have children someday.
Along with Prince Harry, they are expected to play a prominent role as special ambassadors at the London Olympics.
Harry stands to inherit a similar amount when he turns 30 in 2014.