While things initially got off to a slow start, with both tigers described by the zoo as "cautious", they quickly turned serious and Asim began to get aggressive with his female counterpart.
Male tiger, Asim, was brought to the zoo from a Danish safari park, with the intention of introducing him to long-term resident, Melati.
Contingency plans called for handlers to use loud noises, flares and alarms to try to distract the tigers, but that didn't work. But after they were put together for the first time in the zoo's 2,500 sq m Tiger Territory enclosure, which replicates their natural Indonesian habitat, Asim became aggressive. After their keepers saw positive signs, they decided to make the "high-risk" introduction on Friday morning.
"This morning, the two tigers were in separate paddocks and the adjoining door was opened to allow them to meet".
Asim and Melati were matched through the European Endangered Species Program for Sumatran tigers, which seeks to rescue the cats from near-extinction, the zoo said.
The zoo noted that introductions of big cats to one another are always considered to be high risk.
Melati in Tiger Territory. Credit ZSL London
Asim was secured and removed to another paddock, but vets couldn't save Melati who had died.
Ten-year-old Melati, who had been at London Zoo since 2012, was mauled by Asim shortly after they were introduced and could not be saved, despite the efforts of staff.
Ahead of Asim's arrival, the zoo described the large cat as "handsome", "confident" and said he was "known for being very affectionate with the ladies in his life - we're hoping he'll be the ideal mate for our lovely Melati".
Meet our latest arrival ❤️ Seven-year-old Asim, whose name means "Protector" in Arabic, has moved from @ReeParkSafari.
"With just 400 critically endangered Sumtran tigers remaining in the wild, it's important that tigers like Jae Jae (the zoo's former male tiger) and Melati are given the opportunity to have cubs with other mates - to ensure genetic diversity across the world's zoos and ultimately safeguard the future of the species", she said in a statement.
Sumatran tigers are the smallest surviving tiger subspecies and are distinguished by heavy black stripes on their orange coats, according to wildlife conservation non-profit WWF.