Sophie Grimaldi (formally Princess Sophie of Monaco) is the mother of Louis and Beatrice Grimaldi, and short time mother in law of Blair Waldorf. As a recurring character, Sophie appears in the fourth and fifth seasons only. She is portrayed by Joanne Whalley.
Sophie makes her first appearance in The Princesses and the Frog to confront Louis about publicly dating Blair, who is a commoner from America. She tells him that it's inappropriate since he is about to become engaged. To punish him, she plans a ball for the next day where he will meet girls she has approved of and he will be forced to pick one to be with. However, he convinces her to meet Blair but before she does, Serena gives her a book full of Gossip Girl blasts on Blair's wrongdoings. After meeting with Blair, she agrees to give her a chance. At the ball, Chuck shows up drunk and causes a scene. Afterwards, Sophie orders Louis to end his relationship with Blair but he proposes anyway. Over the next few days, Blair tries to win Sophie's approval, but Sophie has her followed and learns she's still visiting Chuck. At an engagement party hosted by Eleanor and Cyrus, she chats with Cyrus; who talks up Blair. Sophie decides to give Blair a chance and agree to let her and Louis make their first formal appearance at the Constance/St. Jude's party (Shattered Bass).
In the premiere Yes, Then Zero, Blair is becoming increasingly frustrated with Sophie making all the decisions for the wedding. Louis is afraid to stand up to her, including when Sophie tells Blair to wear her wedding dress and forbids her from choosing her own. After helping Dan save Blair from public humiliation, he begins to stand up to her. After a few months, Sophie returns with her daughter Beatrice, and they learn of Blair's pregnancy. Sophie is delighted by the news and agrees to stay for the Waldorf's Yom Kippur dinner. Sophie is adamant about Blair raising her child exclusively in Monaco under traditional Monégasque royalty rules. Blair originally fights this idea, until she feels abandoned by all her friends in New York. Meanwhile, Eleanor plants the idea of a custodial contract into Sophie's head, and she has one drawn up. Wanting to take the throne for herself, Beatrice sabotages the contract and adds in extreme clauses. However, upon learning what she did, Sophie decides to keep the clauses so she'll know once and for all if Blair really means well for the family. Lois becomes outraged, and Sophie beings to ice him out, choosing to focus on Beatrice (The Fasting and the Furious).
In G.G., Sophie arrives in New York to attend the wedding. The morning of, she warns Louis that all relationships are business and he's lucky Blair is so advantageous to him. Her point about relationships being business is proven right after the video of Blair declaring her love for Chuck comes out at the wedding. She tells Louis to pretend to be happy and continue with the wedding, as to not cause a scandal. He does so, but is so angry that he tells Blair that he no longer loves her at the reception. Afterwards, she goes with Louis to track Blair down after she runs away from the reception. She plays nice with Eleanor, Lily, and Rufus, but only until she finds they don't know where Blair is. She eventually tracks them her down in an airport hotel, and reminds her about the dowry; and that if she defaults on the marriage so soon, the Waldorf's will be forced to pay it, which would effectively bankrupt them. Not wanting to ruin her family's financial future, Blair agrees to go with her back to Louis. This is Sophie's last appearance in the show (The Backup Dan).
- She has lots of blackmail on the Royal Court of Monaco.
- She is very interested in ornithology (the study of birds).
- She loves to eat salmon.