A mother and her two young children were among at least eight Brits killed when a series of blasts ripped through churches and luxury hotels in Sri Lanka.
Anita Nicholson, 42, her 14-year-old son Alex and 11-year-old daughter Annabel were dining in the Shangri-La hotel in Colombo when a bomber struck.
They have been confirmed as among at least 290 people who died in the massacre on Easter Sunday.
Husband Ben Nicholson survived. Confirming news of their deaths, he said: "Mercifully, all three of them died instantly and with no pain or suffering."
According to her LinkedIn profile, Mrs Nicholson was based in Singapore as managing counsel at the mining and metals company Anglo American.
Mr Nicholson said his wife and children were killed while sitting at a table of the restaurant at the Shangri-la hotel.
"I am deeply distressed at the loss of my wife and children. Anita was a wonderful, perfect wife and a brilliant, loving and inspirational mother to our two wonderful children," he said.
"The holiday we had just enjoyed was a testament to Anita's enjoyment of travel and providing a rich and colourful life for our family, and especially our children.
"Alex and Annabel were the most amazing, intelligent, talented and thoughtful children and Anita and I were immensely proud of them both and looking forward to seeing them develop into adulthood. They shared with their mother the priceless ability to light up any room they entered and bring joy to the lives of all they came into contact with."
He added: "I would like to give my sincere thanks for the medical teams at General Hospital, Colombo, for treating Anita, Alex and Annabel with great dignity and me with kindness and sympathy.
"I would also like to thank the teams at the British High Commission and Adhvan Tours who have looked after me since Sunday morning and the Sri Lankan people I have encountered in Colombo following this catastrophe.
"Anita, Alex and Annabel leave behind a large extended family and many close and cherished friends who are now grieving this tragic loss. We shall all miss them dearly."
It also emerged on Monday morning that Danish billionaire Anders Holch Povlsen lost three of his four children in the attacks.
Mr Holch Povlsen is the largest stakeholder in online fashion retailer ASOS and is believed to be the largest private landowner in Scotland after buying a string of estates.
Confirming the Brit death toll, Sri Lankan High Commissioner to the UK, Manisha Gunasekera, told BBC Radio 4's Today programme: "As of now I think there is information on eight nationals who have lost their lives and the other numbers are of other nationals."
Ms Gunasekera said the investigations were moving "very swiftly" but warned against taking a "linear view" on the motive of the attacks.
She said: "This cuts across the ethnic and religious dimensions... it's very difficult to see who has been targeted. It appears as if the entirety of Sri Lanka has been targeted as well as the unity and coexistence that Sri Lankans have attempted so hard to safeguard over the years."
It came as Hampstead and Kilburn MP Tulip Siddiq said she had lost a relative in the attacks.
She posted on Twitter: "It's all so devastating. Hope everyone is keeping safe. Solidarity with the people of Sri Lanka."
I lost a relative today in the Sri Lanka attacks. It’s all so devastating. Hope everyone is keeping safe. Solidarity with the people of Sri Lanka.— Tulip Siddiq (@TulipSiddiq)April 21, 2019
Police and security services in Sri Lanka are continuing to investigate the blasts, mostly thought to be the work of suicide bombers.
They are being treated as a terrorist attack by religious extremists and police have arrested 24 people, but there was no immediate claim of responsibility.
Foreign Secretary Jeremy Hunt said there was "lots of speculation at the moment but there is no hard knowledge" about the perpetrators of the atrocity and "we obviously need to wait for the police in Sri Lanka to do their work".
He said the UK would offer Sri Lanka support in the days to come.
"If there is any help that the UK can give, we would want to give it," he said.
One line of inquiry will be asking what intelligence services knew about the attack, with Minister for Telecommunications Harin Fernando tweeting: "Some intelligence officers were aware of this incidence.
"Therefore there was a delay in action. What my father heard was also from an intelligence officer. Serious action need to be taken as to why this warning was ignored."
In Colombo, St Anthony's Shrine and Shangri-La, the Cinnamon Grand and Kingsbury hotels were targeted in the first wave of explosions shortly before 9am local time as worshippers attended morning services and tourists enjoyed their breakfasts.
Brits caught up in the carnage in Colombo described the horrific scenes they witnessed.
Following the blast at the Cinnamon Grand, NHS doctor Julian Emmanuel, from Surrey, told The Sun: "I've never seen such utter devastation."
He added: "My children and wife are traumatised by what they saw today. We will never forget this.
"We will always remember Easter Sunday for this reason now."
Kieran Arasaratnam, a professor at Imperial College London Business School, was staying at the Shangri-La.
"Everyone just started to panic, it was total chaos," he told the BBC. "I looked to the room on the right and there's blood everywhere.
"Everyone was running and a lot of people just don't know what was going on. People had blood on their shirt and there was someone carrying a girl to the ambulance. The walls and the floor were covered in blood."
Prime Minister Theresa May said the Easter Sunday massacre was "truly appalling", and "no-one should ever have to practise their faith in fear".
Three Britons and two holding joint US and British nationalities were killed, Sri Lankan authorities said.
Mr Hunt said the death toll of five Britons killed in the attack was "the latest figure that I have heard".
"But obviously our High Commissioner is working on this with his team in the embassy in Colombo, working around the clock, and we are trying to gather as much information as we can about this," he said.
He said the terrorist attacks were "absolutely devastating and despicable" and "for this to happen on Easter Day is something that will shake people around the world, of all faiths and none, to the core".
The acts of violence against churches and hotels in Sri Lanka are truly appalling, and my deepest sympathies go out to all of those affected at this tragic time.
We must stand together to make sure that no one should ever have to practise their faith in fear.— Theresa May (@theresa_may)April 21, 2019
At around the same time as the blasts in Colombo, explosions were also reported at St Sebastian's Church in Negombo and at Zion Church in the eastern town of Batticaloa.
A few hours later, two more blasts occurred just outside Colombo, one of them at a guesthouse, where two people were killed, the other near an overpass.
Three police officers were killed during a search at a suspected safe house on the outskirts of Colombo when its occupants apparently detonated explosives to prevent arrest.
Authorities said at least 290 were killed and more than 500 injured in the attacks.
A curfew was imposed by the authorities on Sunday night and social media use was also restricted by the authorities, which claimed the move was to prevent the spread of false information.
Labour leader Jeremy Corbyn called for "unity, love and respect" to combat hatred.
He said: "I'm appalled by the horrific attacks in Sri Lanka, on Easter Sunday, the most important day in the Christian calendar."
Archbishop of Canterbury Justin Welby said: "On this holy day, let us stand with the people of Sri Lanka in prayer, condolence and solidarity as we reject all violence, all hatred and all division."
Sri Lanka's prime minister Ranil Wickremesinghe condemned "the cowardly attacks on our people".
Nisanga Mayadunne, who studied at the University of London according to her Facebook profile, and her mother Shantha - a TV chef - were also reported to be among the dead.
Nisanga posted a photo of her family eating breakfast in the Shangri-La on Easter Sunday.
Britons in Sri Lanka who need help were urged to call the High Commission in Colombo on +94 11 5390639, while people in the UK worried about friends or family should call the Foreign Office on 020 7008 1500.