Martin Luther King Jr. would have turned 88 on Sunday, and as America celebrates his legacy Monday during the national holiday named for him, a tweet his daughter posted on his birthday is making the rounds, Mashable reports. "Happy birthday dad, I miss you! #MLK," Bernice King tweeted Sunday, including a photo of her leaning her head into the head of her father's monument in Washington, DC. Bernice King, the youngest daughter of King and his wife, the late Coretta Scott King, also appeared on Good Morning America Monday to talk about her mother's new posthumous memoir, calling her "the architect of this King legacy," per ABC News. "What we know of my father really came from her resilience, her determination, her faith, her courage," Bernice King told Robin Roberts. (The city of Biloxi renamed MLK Day—and people weren't happy.)