Beatrice Grimaldi (formally Princess Beatrice of Monaco) is the only daughter of Sophie Grimaldi and the younger sister of Louis Grimaldi. As a member of the Grimaldi family, Beatrice is also a princess of Monaco. She is portrayed by Roxane Mesquida.
Beatrice makes her first appearance in Beauty and the Feast, to accompany Louis back to Monaco for a feast. That same day, Blair is battling morning sickness and is ecstatic to have some time to herself and recover. However, Beatrice has a different plan and informs Blair she moved her flight to the evening so they can spend all day together. On their outing, Beatrice confides to Blair that she's fine not being the reigning sibling and is happy to let Louis have the spotlight, as it's too much pressure. Due to her morning sickness, Blair keeps leaving to find a bathroom and Beatrice suspects something is up. She later concludes that Blair has a drug problem, then bulimia. She tries to tell Louis, but he refuses to believe it. In order to prove it, she has the feast moved to New York. At the feast, Beatrice forces Blair to try food, and when Blair confesses to Dan that she's pregnant, Beatrice overhears; but agrees to keep her secret. At the end of the episode, it's revealed that Beatrice is working with Father Cavalia, the royal family's priest, to take the crown from Louis.
In The Fasting and the Furious, when Blair and Louis reveal the pregnancy to their families, Beatrice tries to use it to her advantage. She eventually makes a deal with Diana Payne: that if Diana helps her get the crown, she'll give her an inside story about the royal family. She sabotages Sophie's contract for Blair, and adds in very controlling clauses to make sure Blair doesn't sign it. However, Sophie finds out she added them in, but decides to keep them anyway. When Blair and Louis again refuse to sign, Sophie tells Beatrice that she's no longer going to be overlooked in favor of Louis.
Beatrice makes her final appearance in Father and the Bride. Blair tells Beatrice she's invited to her bachelorette party, as she's decided she can be a bridesmaid. She informs her that Serena planned a tame event, dinner and a spa evening. Meanwhile, Father Cavalia finds out when Blair goes to confession that she's still in love with Chuck. He tells Beatrice, and instructs her to get Blair drunk and cause a scandal. When out shopping, Blair and Beatrice spot Chuck following them and Blair decides that maybe a wild party might be a good idea, held where Chuck can't find her. In order to get Blair drunk, she sets up a game with Blair and her minions and they succeed in getting her drunk. She reveals to Beatrice, that while she loves Chuck, Louis is the right choice. Later that evening, she gets arrested after police officers see her with a joint, and Beatrice bails her out. She also reveals she bought the cell phones off everyone who recorded Blair's arrest, so the story never gets out. Blair thanks her and Beatrice informs Father Cavalia that she can no longer go through with the plan. As a result, Father Cavalia tells Sophie that Beatrice would benefit from some missionary work in South Africa, and she's never seen again.
In G.G., Georgina Sparks pretends to be Beatrice making a surprise reappearance at Blair and Louis' wedding, but it doesn't come to fruition.