Prince Charles has paid tribute to British forces fighting in Afghanistan in a Christmas radio broadcast to troops serving overseas.
Charles thanked the servicemen and women for their relentless courage and said the nation owed them "an everlasting debt of gratitude".
In his message, recorded last week at St James's Palace and aired on Boxing Day, the prince said all those stationed abroad were very much in his thoughts and prayers.
He added: "I also wanted to pay tribute to the extraordinary contribution made by those of you who belong to our Armed Forces, in all sorts of different parts of the world.
"Nowhere is your fortitude and relentless courage more clearly on display than in Afghanistan, where your resilience, patience and determination to see the job through - usually in impossibly difficult conditions and circumstances - is, quite simply, humbling."
He also joked about receiving a letter from his son, Prince Harry, an Apache helicopter co-pilot gunner serving with the Army Air Corps, who has been stationed at Camp Bastion since September.
"I am well aware of the discomfort and privations you all endure with seemingly endless reserves of good humour," he said.
"In addition to the intense heat and dust of the summer and the freezing winters, you face the constant, terrifying threat of IEDs (improvised explosive devices), attacks from rockets, grenades and small arms fire almost every day - and sometimes these attacks come from infiltrators hidden among those who are supposed to be working alongside you as allies.
"And yet you all seem to bounce back in an almost unbelievable way, despite the setbacks and vicious insurgent attacks."
He added: "With two sons currently serving in the Armed Forces, one of whom is with you all out there, I really do have at least some understanding of what your loved ones on the 'home front' are going through."
He said servicemen and women could keep in touch with relatives through phone calls and the internet "or, in the case of my younger son, to receive a very rare and precious letter in answer to mine".