Prince Harry joined the loved ones of Britons killed in terror attacks in Tunisia at a special memorial service at Westminster Abbey.
Harry laid a wreath at the Innocent Victims Memorial on behalf of his grandmother the Queen as he gathered with survivors and families affected by the two atrocities in 2015.
He also delivered a reading during the central London service, which was conducted by the Dean of Westminster, the Very Reverend Dr John Hall, and attended by David Cameron.
Members of public looked on outside the Abbey as Harry, wearing a dark blue suit, laid the wreath of white flowers before rising and bowing his head in a moment of silent reflection.
The circular stone and slate memorial was unveiled by the Queen in 1998 and created to remember victims of war, violence and oppression across the world.
During the service, Harry and the Prime Minister both read Bible passages, from Revelations and Isaiah respectively, before the 900-strong congregation.
Dr Hall said: "We remember with thanksgiving those whose lives were brutally cut short.
"We honour the courage of those who survived and the families of those who suffered.
"We share our grief with victims of attacks from other countries and their families."
He said many of those attending sought the answer as to why the attacks happened, adding he did not believe the deaths were fated or were "an act of God".
"People have to choose and have the freedom to choose. Some will follow the way of light and peace. Tragically others will follow the way of darkness and destruction," he said.
"Our prayer today is for the defeat of darkness and destruction and that light and peace may have the victory."
Thirty Britons were among 38 people massacred in the Tunisian resort town of Sousse in June last year - the worst incident of terrorism involving British people since the July 7 attacks in London in 2005.
Gunman Seifeddine Rezgui targeted holidaymakers on the beach and in a hotel before being shot dead by security forces. Terror group Islamic State (IS) claimed responsibility.
Among those killed was engineer Stephen Mellor, from Bodmin, Cornwall, who died as he shielded his wife Cheryl.
Three generations of one family also died when Joel Richards, 19, a University of Worcester student and talented football referee, and his uncle Adrian Evans, 49, and grandfather Charles "Patrick" Evans, 78, were gunned down. Joel's teenage brother Owen survived the attack.
Three months earlier, IS terrorists opened fire on tourists at the Bardo National Museum in the capital Tunis. British tourist Sally Adey, 57, from Shropshire, was among 22 people killed.
Family and friends of the victims placed 31 candles on the Abbey's altar in memory of each of those who died, before their names were read aloud by BBC security correspondent Frank Gardner.
Mr Gardner, himself shot by terrorists in 2004, also spoke during the service about his experiences.
He said: "The scars that we carry for things like this are in your head, more than anywhere else."
He added his daughter had taught him an important lesson, when she told him: "Dad, the people who did this to you, they are dead or in prison but you get to come on holiday with us."
The congregation sang the National Anthem to draw the memorial to a close.
Harry met with Abbey staff and Mr Gardner as he left the service.
The Government is to fund a permanent memorial dedicated to the victims of the Tunisian beach massacre, as well as creating a separate site of remembrance for all British nationals killed in terrorist atrocities overseas.
After the service Mr Gardner said it had been an "incredibly dignified occasion".
"It was moving, it was solemn without being morbid, it was managed and organised to perfection," he added.
"I really hope that everybody there and all the survivors, the relatives - the people who knew the victims personally - will get some sense of comfort from this.
"It is an opportunity to remember their lives, to celebrate their lives - these are people who chose to go to what should have been a sunlit country - only to be slaughtered in this pointless act of violence."
He said the prevailing theme of the service was that "good must triumph over evil" and called the address by the Dean of Westminster "bonding".
"The most poignant thing for me was the silent procession of 31 candles carried by the loved ones of people who died," said Mr Gardner of the service.
He added: "I was there absolutely as a fellow victim of terrorism. It was quite emotional for me."
Survivor Samantha Richards, 43, from Northwich in Cheshire, was at the service with her two sons Thomas, 22, and Callum, 17.
The trio were forced to flee the beach when the gunman opened fire, and both Mrs Richards and her eldest son were later injured by shrapnel from a grenade blast inside the hotel.
Of the service, Mrs Richards said: "I think it's towards closure, to try and get on with the rest of our lives really.
"It will never go away, it will always be here but it was just nice to remember it today and those people that died."
Richard Paciukanis, 60, also attended with his wife Bernadette.
The couple had been out in Tunisia for her 57th birthday when the gunman struck, and Mrs Paciukanis described a bullet narrowly missing her head as she fled down a corridor in the hotel.
The couple, from Halifax, Yorkshire, said they found the lighting of the candles "moving".
"It's helped a little bit - I think this is maybe part of the ending. It will never be the ending but it has helped," Mr Paciukanis said.
"It was my birthday that day so it will always be there," Mrs Paciukanis added.
"The bereaved that came through with the candles was very nice, very moving."