Prize-winning architect Mr Langdon, 33, is one of six Britons killed as gunmen stormed Nairobis Westgate Mall on Saturday, whilst his heavily pregnant 33-year-old Dutch partner is one of the 62 to lose their lives in total.
As the siege entered its third night, it emerged that a mother and daughter from Leamington, Warwickshire, were gunned down on their shopping trip.
Zahira Bawa, 41, and eight-year-old daughter Jennah were named locally as victims. Her husband Louis, 43, a marketing executive, had to wait outside the mall for more than 24 hours and learned of the deaths of his wife and only child when paramedics showed him a photograph of their bodies.
The mother of Mr Langdon yesterday paid tribute to her son.
She wrote on Facebook: "We have lost my beautiful son Ross Langdon, his lovely partner Elif Yavuz and their much loved baby just two weeks away from birth. The loss is immeasurable, absurd and excruciating."
The couple, who lived in countries across East Africa, travelled to the Kenyan capital to use its better-equipped medical facilities for their babys birth.
Mr Langdon, a dual citizen born in the Australian state of Tasmania, worked on projects throughout Africa where he designed an HIV-Aids hospital for free.
He was a founding director of Regional Associates, an architecture firm with offices in London and Melbourne.
Lifelong friend Peter Adams, an artist and writer from Tasmania, said he and Harvard-educated malaria specialist Dr Yavuz had dedicated their lives to trying to create a peaceful world.
"You talked to the two of them and you would feel hopeful", he said.
"They were so happy. You know when people are happy and in love. They symbolised to me what everybody would want in their life a good relationship, good work, a good sense of confidence about who they are. They had all three."
He added: "Both had dedicated their lives to working for a peaceful world. Both had so much to offer."
Mr Langdon won an award for his work and is said to have designed an opera house in Denmark as well as a Ugandan eco-village that used only local labour.
He spent most of the past four years in Africa, with long stays in London.
Dr Yavuz, born in the Netherlands, worked for the Clinton charitable foundation in East Africa and recently posted a photograph of herself with former US president Bill Clinton on Facebook.
Meanwhile a young British mother was yesterday hailed a heroine of the siege.
The woman escaped the mall with her son and daughter but bravely chose to go back inside to save two more children whose mothers had been murdered. She was shot in the leg and after she made it outside again was taken to hospital, where she is said to be recovering well.
The woman's courage was praised by her family, who asked for her name to be protected for fear of reprisal attacks.
A family member said her husband is just delighted that he isnt burying his wife or babies today, adding: "She displayed immense bravery on the day by asking for her children to be released and then going back for two more whose mothers had been killed, all whilst being shot herself. Inspirational doesnt seem to cover it."
