He's missed sharing with his father "the first day of going to school, having the first girlfriend, being able to drive," Prince testified.
While Paris Jackson's suicide attempt and hospitalization was not brought up in court -- and it is unclear if jurors learned about it in the news -- Prince did speak about his sister.
"I think out of all of my siblings she was probably hit the hardest because she was my dad's princess," he said.
Prince said the questioning of Paris by AEG Live lawyers over two days in March was painful for her. "She had some problems before, after and, I assume, during," he said.
"She definitely is dealing with it in her own way," her brother said.
Paris, who was 11 when her father died, is not available to testify in person in court because she is hospitalized for psychiatric treatment.
While he and his sister no longer want to celebrate birthdays because "it's not the same without" their father, Blanket, now 11, does, Prince said.
"Right now, I don't know if Blanket realizes what he lost," he said. "He was so young. He is still growing up just like I am and he doesn't have a father to guide him."
AEG Live attempted to compel Blanket, the youngest child, to testify, but the judge rejected its request after a psychologist said it would harm the boy.
Changing the world?
Jurors watched a home video of Michael Jackson questioning his three children about how they planned "to change the world" when they grow up.
Prince testified that the video was made at Christmas.
"What's Christmas mean?" Jackson is heard asking his children.
"Love," Blanket responded.
"Who's Blanket going to be to change this world?" Jackson asked.
"I don't know," Blanket, who appeared to be about 5 at the time, answered.
"What does Paris want to do? Be honest search your heart," Jackson said.
"Help the poor," she answered. Paris also said she would like to be a gymnast.
Prince told his father he aspired to be a movie director and architect because he liked "making things."
Private details revealed