Did Charles really sound 'giddily elated' after Diana died?

Almost thirty years after her death, there's new commentary about Princess Diana and the reaction of her former husband. Charles Spencer, the brother of the late Princess of Wales, is releasing a memoir called Swan Song: Diana, My Sister. It includes some bombshell claims about King Charles, including that he sounded 'giddily elated, like a lottery winner' in a phone call to Earl Spencer. It's forced an unusual rebuke from the Palace.