Call me sweetie? The secret nicknames of King Charles and Princess Kate for each other revealed

Princess Kate calls King Charles 'Grandpa' and he calls her 'darling daughter-in-law,' according to sources cited by RadarOnline. Biographer Robert Jobson described the warmth between them and Catherine's role as a unifying factor in the royal family.

Princess Catherine, known as Kate Middleton, and Britain's King Charles have developed a warm relationship behind palace doors, according to sources who spoke to RadarOnline. According to the report, Catherine often calls her father-in-law 'Grandpa,' while he affectionately addresses her as 'darling daughter-in-law.' Royal author Robert Jobson previously revealed these terms of endearment in his biography 'Catherine, the Princess of Wales,' and described how the king greets Catherine with a kiss and exchanges jokes with her at family gatherings. Jobson described Catherine as a 'peacemaker' who helped improve relations between William and Charles. Another source described her as someone who prefers to resolve tensions with patience and understanding. Catherine's status has evolved since her marriage in April 2011, and she is taking on increasing ceremonial and philanthropic responsibilities.