A man who met Pc Keith Palmer has said his murder "sent a shiver down my spine" as he shared a photo of himself and his daughters with the officer outside the Houses of Parliament.
In a post on Facebook, Andrew Thorogood, 41, a jeweller from Alice Springs, Northern Territory in Australia, said he had met the "genuinely nice bloke" last year and invited him to visit.
"We were in London last October and visited the Houses of Parliament. An officer by the name of Keith Palmer was happy to pose with us for a photo once he learned that we had travelled all the way from Alice Springs in the Northern Territory, Australia," Mr Thorogood wrote.
"I spoke with Keith for quite a while and found him to be a genuinely nice bloke. He said he would love to visit Australia with his family one day. The girls suggested if he did make it to Australia, he should visit Alice Springs and we would show him how special a place it is.
"That will never happen now, all because he was doing his job and trying to keep people safe in the face of yet another crazy terror attack. Our thoughts are with his wife and family.
"With everyone so suspicious of everyone else these days, he was happy to chat and smile for a photo with a bunch of Territorians on holiday whilst still remaining vigilant and carrying out his duties as a police officer."
Mr Thorogood later told the Press Association: "The last 24 hours have been somewhat surreal. I can't begin to imaging what his wife is feeling.
"It strikes a chord because my wife is from Essex and we have a close affinity with the UK.
"The brief conversation and photo we had with Keith just makes it more personal."
It comes as one of the final photos of Pc Palmer was shared online. The image shows tourist Staci Martin with the officer just 45 minutes before he was stabbed by attacker Khalid Masood, also known as Adrian Russell Ajao.
Ms Martin, on a visit from Florida to London, told ABC News: "It's my first time in London and I see his hat and I'm like 'I have to take a picture of him with his hat'."
"I walked up to him and said 'do you mind if I take a picture?' He said 'no problem'. He was really nice."
Within an hour, the attacker had driven a car into a number of pedestrians on Westminster Bridge, before stabbing and killing Pc Palmer as he entered the grounds of the Palace of Westminster.
Three other innocent victims - Kurt Cochran, Aysha Frade and Leslie Rhodes - have died following the attack, while many more were injured.