Prince William's former nanny sent him a touching note after he told her that his parents, Princess Diana and Prince Charles, were separating, it was revealed at London's Old Bailey Courthouse on Monday in the case of Diana's butler Paul Burrell, PEOPLE reports.

The nanny's letter was found at the home of Burrell, 44, who stands accused of stealing more than 300 items from Diana and Princes Charles and William. Burrell denies the charges.

In Monday's testimony, the former nanny, Olga Powell, said she sent the message to William while he was at Ludgrove prep school in November 1992 -- one month before the separation became public in December 1992.

Asked if it was a personal letter, Powell, replied, "Yes, very personal."

Powell, a white-haired woman with a quiet, no-nonsense manner, worked with the boys from the time William, now 20, was 6 months old until Diana's death in August 1997. She was asked by prosecuting barrister William Boyce, QC, "Is there any reason why Mr. Burrell should have possession of this letter?"

Replied Powell: "No."

As Burrell simply stared forward in the courtroom, Powell outlined what the princes would do with letters they received at school: "They usually left them in their tuck box and brought them home and destroyed them if they didn't want to keep them," she said.

Those letters that the princes wished to keep would be put away in a "cupboard," she added.

The trial continues Tuesday.