The body was recovered near Limehouse, downstream of London Bridge, at around 7.45pm on Tuesday by specialist officers from the marine police unit.
"We are paying a heavy cost in these attacks", Macron said.
Mr Thomas had been missing since he was caught up in the attack with Ms Delcros. Nearly 50 were wounded.
"The attack began at about 10 p.m., local time, when a van crossing London Bridge veered into pedestrians, crashing outside the Barrowboy & Banker Pub".
Police said earlier that witness accounts suggested Thomas might have been thrown into the river.
Relatives of Australian Sara Zelenak have confirmed she was another of the victims of the weekend attack.
At least 13 people have been arrested by the Police suspecting their connection to the attack.
The force says formal identification has not yet taken place, but Thomas' next of kin have been informed. Butt was a 27-year-old British citizen born in Pakistan. They have not been identified or charged. But the 12 others arrested have been released without charge.
On Tuesday the third attacker was named as Youssef Zaghba, an Italian national of Moroccan descent, who was living in east London.
Italian news reports say the London Bridge attacker who had been stopped in Italy en route to Syria a year ago was subsequently listed in the European-wide intelligence-sharing system and was stopped at London's Stansted airport in January but let go. "But I did my best, and I think he was worn down on the inside", she said. "It's as if I were ashamed to say 'I'm also a mother, I'm also suffering".
The terror unfolded at around 10pm when the attackers drove a hired van onto the pavement, hitting several people, before launching a knife attack in the Borough Market area.
Shahid allegedly provided al-Qaida terror training to Mohammed Siddique Khan, one of the four suicide bombers who killed 52 people during London's morning rush hour in 2005.
Butt, Redouane and Zaghba were shot dead at the scene of the attack by officers within eight minutes of police receiving the first emergency call.
The other two attackers were identified as Khurum Butt, a 27-year-old whose extremist views had been reported to police, and 30-year-old Rachid Redouane, also known as Rachid Elkhdar, a Moroccan pastry chef. She added that she visited her son in London, and "that neighbourhood did not make me feel comfortable".
Butt was the office manager according to a statement from Auriga Holdings, the holding company.
Butt's family said Wednesday they were "shocked and appalled" by his actions.
He was not a police or MI5 subject of interest. In particular, there are questions over whether investigators had the resources to look into complaints such as those leveled by Butt's neighbors about his attempts to radicalize children and whether crucial opportunities were missed.
He said Zaghba was always tracked by Italian intelligence officers while in the country and that United Kingdom authorities were informed. He was also stopped at London's Stansted airport in January, but let go.
Reaction to the attack has dominated the final days of campaigning before Thursday's general election, with opposition Labour Party leader Jeremy Corbyn and others criticizing May for cutting police numbers by roughly 20,000 during her tenure as home secretary. But he successfully got them back after a court determined there wasn't enough evidence to arrest him.
He was stopped because he was carrying only a small backpack, a passport and a one-way ticket which caused authorities to become suspicious of his intentions.
But an Italian prosecutor said Zaghba was flagged to Britain as a "possible suspect" back in March 2016. Collina said she urged them to detain him and prevent him from going.