What caused the conflict between the Duke of Stanhope and his grandson in the novel, Almost Heaven?

The Duke of Stanhope is an elderly man who, in old age, has come to realize that disowning his son for marrying a woman he disapproved of was wrong and tries to make amends with his grandson. Ian, the Duke of Stanhope's grandson, does not wish to forgive his grandfather. However, when Ian realizes he needs his grandfather's standing in society to help Elizabeth, he agrees to accept the title his grandfather offers, but does not want his money. The Duke of Stanhope tricks Ian into accepting the money anyway. The Duke of Stanhope then stands beside Ian at a ball to which Elizabeth has decided to make her second debut, causing a stir among the members of society, but also successfully repairing Elizabeth's reputation. The Duke of Stanhope slowly wins his grandson's affections and lives the rest of his long life in his grandson's company.