Titmus won in a time of 1:53.50s ahead of Hong Kong’s Siobhan Haughey with Canada’s Penny Oleksiak third.

Ledecky, the defending gold medallist and five-time Olympic champion, finished a disappointing fifth, 1.71s behind Titmus.

Once again the 20-year-old Titmus, dubbed ‘The Terminator’, delivered a blistering final lap – she had been in third place at the 150m turn with Haughey in the lead.

Titmus had beaten Ledecky to gold in the 400m freestyle on Monday and she becomes the first Australian woman to complete the 200-400 Olympic double since Shane Gould at the Munich 1972 Games.

Ledecky is back in the pool later on today when she competes in the first edition of the women’s 1,500m freestyle.

Titmus and Ledecky are expected to face each other in the 800m freestyle on Saturday in which the American is heavily favoured, and they will also be on opposite sides in the 4x200m relay.

Milak lived up to his billing as the heavy favourite in the men’s 200m fly and won by 2.48s from Japan’s Tomoru Honda with Italy’s Federico Burdisso taking bronze.

The Hungarian’s time of 1:51.25s was an Olympic record, surpassing Michael Phelps’ mark from an event he once dominated.

Phelps had set the previous Olympic record of 1:52.03s in Beijing.

Milak’s world record of 1:50.73s came at the world championships in Gwangju in 2019.

His time might have been even faster if not for a mishap with his swimming trunks.

Showing reporters a ripped pair of trunks, he said: “They split 10 minutes before I entered the pool and in that moment I knew the world record was gone.

“I lost my focus and knew I couldn’t do it … but I am happy with the gold medal.”