LONDON — Letters sent by Britain’s late Princess Diana — including one in which she described a young Prince Harry as being “constantly in trouble” while at boarding school — went up for auction Thursday.

The six handwritten notes were sent to Cyril Dickman, a former head steward at Buckingham Palace, during the 1980s and 1990s.

In one, sent five days after Harry’s birth in September 1984, Diana thanks Dickman for a card he sent and described how affectionate Prince William was toward his baby brother.

“William adores his little brother and spends the entire time swamping Harry with an endless supply of hugs and kisses, hardly letting the parents near!” she wrote.

Diana added that she was overwhelmed by the reaction to Harry’s birth.

“I can hardly breathe for the mass of flowers that are arriving here!” she said.

In another letter, written in 1992, Diana said both her sons were enjoying boarding school, “although Harry is constantly in trouble!”

Diana died in a car crash in Paris in 1997.

The letters are part of a collection that Cheffins auction house in Cambridge said includes about 40 royal memorabilia items that are expected to fetch from 80 to 900 pounds ($99 to $1,110 USD) each.

Other items include photos and Christmas cards from various members of Britain’s royal family, and a boxed piece of cake from Queen Elizabeth II’s wedding in 1947.