Peter Phillips has spoken about the pressure on royal family members to be "out and about" conducting public engagements amid the current health crises.
The King has postponed much of his public facing duties as he undergoes cancer treatment, while the Princess of Wales revealed last Friday that she has started preventative chemotherapy following a cancer diagnosis in late February.
And in a rare televised interview with Sky News Australia, Peter, who is the son of the Princess Royal, was asked about support from external family members.
"Everyone has their own different role to play," he said. "There's a lot of pressure on the Duke and Duchess of Edinburgh, my mother and the Queen to take on a lot more of the responsibilities… that adds its own pressures.
"There is definitely a short-term pressure on certain members of the family to be able to continue to be out and about and to be seen and to support organisations and conduct official engagements that need to be done."
The father-of-two, 46, added that his uncle Charles is "frustrated" that his recovery is taking longer than "he would want it to".
Peter, who is visiting Australia as patron of charity ISPS Handa, which supports disabled sportsmen and women, said the King was "in good spirits", but was "pushing" his staff to be able to return to his duties after beginning treatment for cancer last month.
"I think ultimately he's hugely frustrated," Peter said. "He's frustrated that he can’t get on and do everything that he wants to be able to do. But he is very pragmatic, he understands that there's a period of time that he really needs to focus on himself.
"But at the same time he is always pushing his staff and everybody – his doctors and nurses – to be able to say 'actually can I do this, can I do that?'"
Peter, who is head of partner acquisition for the sports and entertainment rights agency CSM Sport & Entertainment, was not given a royal title by his parents, Princess Anne and Captain Mark Phillips, at birth.
Like his sister and equestrian, Zara Tindall, he has carved out his own career within the entertainment, sports and television industry.
The interview took place before Princess Kate revealed her cancer diagnosis to the world in an incredibly personal and moving video message.
Peter, who is close to his cousin, Prince William and his wife Kate, said of the couple: "She's remarkable in herself… Her and William make a fantastic team together."
Speaking about their family life with Prince George, Princess Charlotte and Prince Louis, he also told Caroline Di Russo: "Their kids are great and they have the balance of public life and trying to be parents to three young children which is always difficult. They've got it pretty right because I think as history has taught us and anyone knows that actually you want to be there for your children."
Peter shares daughters, Savannah, 13, and Isla, who turns 12 on Friday, with his ex-wife, Autumn Kelly.