Rishi Sunak will be the next Prime Minister, succeeding Liz Truss who has resigned after seven weeks in office.
The former chancellor won the support of Tory MPs on Monday and will enter Downing Street less than two months after he lost to Ms Truss in the race to replace Boris Johnson.
Mr Sunak will be the UK's first Hindu prime minister, the first of Asian heritage, and the youngest for more than 200 years at the age of 42.
He saw off competition from Commons leader Penny Mordaunt, a Royal Navy reservist and former defence secretary, who pulled out of the race to become the next PM as she failed to get the 100 nominations from Tory MPs required by the 14:00 deadline, while Mr Johnson also ditched his own comeback bid.
So, where does the next PM stand on defence matters?
Well, in July when running to replace Mr Johnson, Mr Sunak vowed he would never "short-change" the Armed Forces if he became Prime Minister.
However, he described Ms Truss' pledge to boost defence spending to 3% of GDP as "arbitrary".
"Defence spending needs to increase, and I will never short-change our Armed Forces and my track record proves that with the largest increases in defence spending since the Cold War," Mr Sunak said.
"Simply saying 3% [of GDP allocated to defence] isn't a plan, it's an arbitrary target. Rather, we need to provide our military with the resources it needs to do what it needs to do to keep us safe," he added.
In 2019, the Conservatives committed to "exceed the NATO target of spending 2% of GDP on defence and increase the budget by at least 0.5% above inflation every year of the new Parliament".
But with another new prime minister and expected spending cuts, it remains to be seen if that commitment will continue.
On the campaign trail in August, Mr Sunak said he viewed the NATO defence spending target of 2% of GDP as a "floor and not a ceiling" and noted that spending is set to rise to 2.5% "over time", but refused to set "arbitrary" goals.
On Monday, European Research Group chairman and Tory MP Mark Francois told reporters in Parliament that after speaking to the two leadership hopefuls (Ms Mordaunt and Mr Sunak), Mr Sunak did not commit to the 3% target "but said he was determined if he were prime minister that he would spend whatever was necessary to keep the country safe".
According to Mr Francois, Penny Mordaunt went "slightly further".
"She said that her aim was to get to 3% on defence, but when economic conditions would allow," Mr Francois said.
Mr Sunak's commitment to balancing the books is well known and is what saw him hike the tax burden to its highest level for 70 years as chancellor despite his personal preference for lower taxes.
In his first leadership bid, Mr Sunak was already unenthusiastic about large-scale spending commitments.
Reports have also suggested Defence Secretary Ben Wallace would also quit if the spending pledge was scrapped.
Voting records on defence
Here's a look at Mr Sunak's voting records on defence matters, according to the parliamentary website 'TheyWorkForYou'.
So-called Islamic State
The next PM has consistently voted for military action against Daesh (so-called Islamic State or IS) – two votes for, none against, in 2015.
He has voted consistently in favour of replacing Trident with a new nuclear weapons system.
Overseas combat operations
Mr Sunak has voted consistently for the use of UK military forces in combat operations overseas.
Mr Sunak has voted against investigations into the Iraq War.
According to TheyWorkForYou, Mr Sunak has never voted on strengthening the Military Covenant (five absences, in 2020).
The Armed Forces Covenant is a promise by the nation to ensure that those who serve or who have served in the Armed Forces, and their families, are treated fairly.
It covers education and family well-being, housing, careers, healthcare, financial issues and discount services.