Princes William, Harry Remember Late Grandfather Prince Philip In New Documentary [Watch]

Prince William and Prince Harry spoke fondly of Prince Philip in a new documentary about their late grandfather.

Queen Elizabeth II's husband, who was the longest-serving consort of any British monarch, died of natural causes on April 9 at age 99. The Duke of Edinburgh was laid to rest on April 17 in a funeral ceremony that saw the Duke of Cambridge and the Duke of Sussex reuniting for the first time in over a year.

Now, the brothers, as well as other royal family members, are looking back at Prince Philip‘s life and recalling the patriarch's influence in a new trailer for the documentary, "Prince Philip: The Royal Family Remembers."

"He’s always been a huge presence behind everything we’ve done, really," Prince William said in the clip released by the BBC Saturday.

In the trailer, Prince William wore a blue sweater over a button-down shirt with a blazer. Meanwhile, his younger brother opted for a more casual look, sporting a white long-sleeved shirt with the first few buttons left open.

"What you see is what you got with my grandfather. He was unapologetically him," Prince Harry told the cameras.

"You never really prepare yourself for losing him because he was always there," said their 40-year-old cousin Zara Tindall, who is the daughter of Princess Anne and Captain Mark Phillips.

The trailer also showed Prince Philip with a young Prince Charles and Princess Anne by the river. "We were lucky to have him for nearly 100 years," the Prince of Wales said.

The BBC announced the "Prince Philip: The Royal Family Remembers" documentary Wednesday. The film had been planned long ago to mark the 100th birthday of the Duke of Edinburgh, but after his death, it became a memorial.

Meanwhile, Prince William and Prince Harry both paid tribute to their late grandfather shortly after he passed away.

In a statement released on Twitter on April 12, Prince William said Prince Philip's "century of life was defined by service — to his country and Commonwealth, to his wife and Queen and to our family."

He added that he considered himself lucky to have had Prince Philip as an "enduring presence" in his adult life. The prince was also grateful to his grandfather for his kindness to his wife, Kate Middleton, and the special memories his kids had with him.

Prince Harry remembered the late royal as "my grandpa: master of the barbecue, legend of banter and cheeky right ‘til the end." Like his older brother, the Duke of Sussex remembered Prince Philip as "a man of service, honor and great humor."

"Prince Philip: The Royal Family Remembers" will premiere in the U.K. on Sept. 22 at 9 p.m. on BBC One. A U.S. premiere date has not been announced.