Conservative MP Sir David Amess, 69, has died after being stabbed multiple times during a constituency surgery.
Sir David was one of the longest-serving MPs in parliament, and had represented Southend West, Essex, since 1997.
His colleagues responded with horror to the news, describing him as one of "the kindest men in politics".
A father-of-five, Sir David was also a well-known animal lover.
Two weeks ago he announced that he and his beloved three-year-old French Bulldog Vivienne were running in the Westminster Dog of the Year Show.
Watch: Tributes paid to ‘true gent’ and ‘friend to everyone’
He was known for his long-running campaign to make Southend a city.
In December 2019, he secured an adjournment debate in the Commons specifically on the campaign and told MPs: “I am not messing around.
“We have got it from the prime minister that Southend is going to become a city – and it will become a city.”
As a strident supporter of the British monarchy, Sir David asked for a new statue of the Queen for Southend – insisting the Queen deserved one for being a “great” monarch.
He previously represented the constituency of Basildon for 14 years.
One of his most significant achievements in Parliament was the Protection Against Cruel Tethering Act (1988), which came about as a result of his long-standing concern for animal welfare.
He also sponsored the Warm Homes and Energy Conservation Act (2000) which required the secretary of state to "publish and implement a strategy for reducing fuel poverty".
This Act was widely credited with a significant change in both attitude and policy towards fuel poverty within the UK.
In March 2018 Sir David launched an All-Party Parliamentary Group on Endometriosis with the aim of raising awareness of the condition, and to investigate how those who suffer from endometriosis can get the support that they need.
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He has raised the plight of women with endometriosis in many debates and a number of times in Parliament, most recently to highlight the impact of the coronavirus pandemic on endometriosis care and to draw attention to the APPG's report that was launched in October 2020.
Following news of the his death, tributes to "the kindest and nicest man in politics" flooded Twitter.
Health secretary Sajid Javid wrote: "Devastated to learn of Sir David Amess' murder.
"A great man, a great friend, and a great MP killed while fulfilling his democratic role. My heart goes out to Julia, his family, and all who loved him.
"Let us remember him and what he did with his life."
Transport secretary Grant Shapps said: "Awful, tragic news about David. A dedicated, thoughtful man and a true Parliamentarian, who lost his life while serving the constituents who he worked relentlessly for throughout his career.
"My thoughts are with his family and friends at this time."
And Labour MP Lucy Powell wrote: "This is totally heart-breaking. Tragic.
"Such a lovely, decent man who has served his constituents and the country so well for so long.
"I only last met with him a few weeks ago about building and fire safety issues on which he’s tirelessly campaigned for years.
"What a loss."
Carrie Johnson, wife of the prime minister, said: "Absolutely devastating news about Sir David Amess.
"He was hugely kind and good. An enormous animal lover and a true gent.
"This is so completely unjust. Thoughts are with his wife and their children."