Diana is Cliff's biological mother and Callum's stepmother. She has always hated Callum for many reasons. Most importantly, Callum's presence in her family has infuriated her. Furthermore, when Cliff and Callum are compared, Callum is actually superior in every way. That's why Diana doesn't want Callum to usurp the throne as the first heir someday. Furthermore, her husband has always praised Callum, and she has protested, but he never paid attention.
The only way to destroy Callum was to separate him from the woman he loved. That's why, for the past five years, he'd been silent, content with Callum living the life he wanted. He'd been happy to see Callum's restlessness every day, and he'd let Cliff live happily with the woman he loved.
Actually, Diana doesn't hate Edith, but because Edith likes Callum more than Cliff, Edith also becomes a victim of her outburst.
