As the father of two military sons, Prince Charles says he worries "all the time" about Princes William and Harry's safety.
"As you can imagine, being a parent of two boys in the armed forces, I do share with you the worry and anxiety of not knowing the exact details about our children's whereabouts," Prince Charles told a gathering of military members and their families, according to British newspaper the Sun.
He was addressing guests at the Sun's Military Awards Thursday night in London.
"The younger one is at this moment in Afghanistan," he said, referring to Prince Harry, 28. "Fortunately, he rings me every now and then. … And from time to time, I've even persuaded him to write me a letter."
The prince, who himself served in the Navy and Air Force, said he encourages letters over emails or texts because, "In 30 years time or 40 years time, that will be interesting history."
Harry is an Apache helicopter co-pilot and Prince William is a Royal Air Force search-and-rescue helicopter pilot. He praised the "unending relentless courage" of the armed forces as well as the "extraordinary resilience and the unbelievable support" provided by their families at home.
"I really do understand the worry of service families when their loved ones are serving in somewhere like Afghanistan," Charles said, according to the Sun. "It's almost easier for those serving away than for those left behind because you worry all the time."
Prince Charles poked fun at his mischievous younger son by saying, "If I want to see what my children are up to, I look at the front page of the Sun."
Photos of Harry's naked partying in Las Vegas were on the newspaper's cover in August.
The normally conservative prince has been uncharacteristically open about his emotions this week following the news that he is going to become a grandfather.
"I'm thrilled, marvelous," Prince Charles, 64, said Thursday. "It's a very nice thought of grandfatherhood in my old age, if I may say so. So that's splendid."