LONDON — Rishi Sunak has promised to “fix” the economic mess wrought by his predecessor Liz Truss after being appointed the new U.K. prime minister.

In a sombre speech on the steps of No. 10 Downing Street Tuesday, Sunak said “mistakes were made” by his predecessor and that he had been appointed “in part, to fix them.”

Truss only took office as U.K. PM last month but was swiftly forced to resign after her radical economic plan spooked the markets, sent Sterling plunging and U.K. borrowing costs through the roof.

Sunak had predicted precisely these consequences during a summer-long Tory leadership contest — in which he finished a distant second place — and is now reaping the political reward.

“Our country is facing a profound economic crisis,” Sunak said, in his first major speech as PM. “I will place economic stability and confidence at the heart of this government’s agenda. This will mean difficult decisions to come.”

Sunak takes over at an intensely challenging time for the U.K. economy, with surging energy costs, mortgage rates and inflation triggering a cost-of-living crisis for millions of households and businesses. Britain also has yawning budget deficit, and Sunak’s new administration is expected to confirm a package of tax hikes and spending cuts in an emergency budget statement next week.

But the new PM insisted he was “not daunted” by the challenges ahead, adding: “I know the high office I have accepted, and I hope to live up to its demands.”

Sunak, 42, is the youngest British prime minister in modern history, and the first British-Asian to lead the country. He was formally invited to form a government by new British monarch King Charles III on Tuesday morning, after winning the second Conservative leadership contest of the year the previous afternoon.

In his speech, Sunak also took a veiled swipe at predecessor-but-one – and former boss – Boris Johnson, who also forced to resign in July over a string of personal scandals.

“This government will have integrity, professionalism and accountability at every level,” Sunak said.

Johnson tweeted his congratulations immediately after Sunak took office, insisting it was “the moment for every Conservative to give our new PM their full and wholehearted support.”

Sunak is expected to spend Tuesday afternoon forming his new Cabinet and appointing key staff to No. 10 roles.

Outgoing PM Truss said in her farewell speech on Tuesday that it had been “a huge honor” to lead the nation, and showed few signs of contrition over her chaotic seven weeks in office.

“From my time as prime minister, I am more convinced than ever we need to be bold and confront the challenges that we face,” Truss said defiantly.

She even quoted the Roman philosopher Seneca, adding: “It is not because things are difficult that we do not dare. It is because we do not dare that they are difficult.”

Sunak won the latest Conservative leadership race after his rival Penny Mordaunt failed to secure the required 100 nominations from her fellow Conservative MPs to make it onto a head-to-head ballot. He also beat off a brief challenge from former PM Johnson, who decided to pull out of the contest Sunday night despite claiming to have enough nominations to make the cut.

Despite his relative youth Sunak is well known to the British public, having served as chancellor for more than two years under Johnson before quitting in July over his former boss’ personal conduct.

He became a wildly popular figure with the general public soon after his appointment in February 2020, after setting up a multi-billion pound scheme to protect people’s salaries if their companies were struggling to keep them on during the COVID-19 pandemic.

But his approval ratings took a massive hit earlier this year after it emerged his wife Akshata Murty held a highly privileged “non-domiciled” tax status in Britain, which she later renounced. He was also criticized after it was revealed he until recently continued to hold a U.S. green card, allowing him to live and work in America — allowing opponents to suggest he might not have been fully committed to remaining in Britain.