Michael Jackson’s eldest son is due to testify Wednesday in his family’s megabucks wrongful death trial — four years and a day after the King of Pop’s shocking fatal overdose.

Prince Jackson, 16, is expected to give emotional testimony about what he saw and heard in the days leading up to the tragedy of June 25, 2009, and how the loss of the only parent he ever really knew devastated his family.

“This trial is about people, and he’s suffered greatly,” family lawyer Brian Panish told the Daily News outside court Tuesday.

Jackson family matriarch Katherine Jackson is suing AEG Live for damages estimated at more than $1 billion, arguing the promoter behind Michael’s ill-fated “This Is It” tour put its desire for massive profits ahead of the “Thriller” singer’s health and safety.

Katherine, the co-guardian of Michael’s three kids, claims AEG hired a debt-ridden doctor in May 2009 and then made it clear the physician would forfeit his $150,000-per-month salary if Michael failed to perform.

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The ruling Tuesday came on the fourth anniversary of Michael Jackson’s overdose death.

The physician, Dr. Conrad Murray, is now serving four years after being convicted of involuntary manslaughter for recklessly providing Michael with a deadly dose of the anesthetic propofol. Michael was taking the surgery strength anesthetic as a sleep aide under Murray’s care.

AEG Live has denied any wrongdoing, saying it was Michael who hired Murray.

Somber fans marked the anniversary of the Gloved One’s death Tuesday by making their annual pilgrimage to his final resting place at Forest Lawn cemetery in Glendale, Calif. They left scores of bouquets outside Michael’s private mausoleum.

“Thinking about my brother on this day. Thank U everyone 4 your love and support and 4 the beautiful display of flowers at Forest Lawn,” Randy Jackson wrote on Twitter.

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Prior to her June 5 attempted suicide Paris Jackson, 15, had been spending more time with her biological mother, Debbie Rowe.

Katherine wore a floor-length black dress to trial Tuesday and sat quietly as a medical expert testified about conflicts of interest.

“It’s a hard day (for Katherine),” Katherine’s personal lawyer Sandra Ribera told The News.

Trent Jackson, the nephew who acts as Katherine’s regular bodyguard, draped his arm around her chair and squeezed her shoulder as an AEG lawyer grilled the expert about Michael’s reluctance to visit a hospital before his death.