Princess Diana's brother, Charles Spencer, intends to marry his longtime girlfriend, former elementary schoolteacher Caroline Freud, on Dec. 15, a spokesman for Spencer said on Sunday. Spencer, 36, has four children from his first marriage, to former model Victoria Lockwood, 35: Kitty, 10, twins Eliza and Katya Amelia, 8, and Louis, 7. Married in 1989, Spencer had seen his tempestuous romance with Lockwood become frequent tabloid fodder, PEOPLE reported earlier this year. During the course of their open-court divorce in 1997, Lockwood's lawyers painted Spencer as a "serial adulterer." Spencer, in turn, claimed that the marriage dissolved as a result of his wife's "mental and physical health," a reference to her struggles with anorexia and alcoholism. Ultimately, the pair agreed to a settlement in which Lockwood received $2.5 million, a sliver of his estimated $131 million fortune. Freud has two children from her marriage to Matthew Freud, who now is married to Elizabeth Murdoch, daughter of media baron Rupert Murdoch. Spencer and his fiancée have known each other since they were students at Oxford University. The quiet family ceremony is to take place at Althorp, the Spencer family's historic home, where Princess Diana was buried following her fatal 1997 car crash in Paris.