Former NDP MP Paul Dewar has been diagnosed with brain cancer, according to a post on his Facebook page Saturday morning.

“While this cancer is devastating news, I am going to pursue the next phase of my treatment with determination, passion and an appreciation for life,” Dewar wrote. “Since I received this diagnosis I have had incredible treatment from smart and caring medical professionals who are completely dedicated to their patients.”

In January, the 55-year-old former Ottawa Centre MP noticed a pain in his arm that wouldn’t go away.

A hospital visit at the beginning of the month revealed that a brain tumour was causing the discomfort. He had surgery to remove the tumour on Wednesday and his treatment is ongoing.

He thanked his family and friends for their “phenomenal support.”

Members of the party were shocked and upset when they heard the news.

“Paul was my mentor,” said NDP MP Guy Caron. “It’s terrible news, but he’s a fighter…I think he knows that we all support him and we all love him.”

Karl Bélanger, who worked for the party for 19 years and left his position as NDP national director in 2015, had nothing but good thoughts for Dewar.

“(I) can only wish him the best as he goes through this,” he said. “He was a great member of Parliament and he’s a great member of his community.

“I know a lot of people will be rooting for him.”

Dewar left a mark in his time on the Hill, and has a legacy for being a party stalwart among NDP MPs new and old.

“As new MPs, we always aspired to be like Paul Dewar,” rookie NDP MP Gord Johns said.

“He showed up. That’s what Paul Dewar did – he showed up for everybody.”

New NDP MP Alistair MacGregor echoed Johns’ thoughts.

“He just made us all really proud,” MacGregor said. “We didn’t know him personally but we always held him up as an example. So it’s very sad news.”

At the NDP Convention in Ottawa Saturday morning, NDP MPs Charlie Angus and Hélène Laverdière shared the news on the convention stage.

.@CharlieAngusNDP & @HLaverdiereNPD on news that @PaulDewar has brain cancer: “He has served our party, this city & this nation with such integrity. And we are here to pray for him and his family for full recovery — to let him know how much we love him & his family & his work.” pic.twitter.com/R39jF3Rucw — CPAC (@CPAC_TV) February 17, 2018

“If you want to help in any way, Paul says to help someone around you,” Angus said.

Angus also asked the delegates to give Dewar’s family time and privacy.

Messages of support have flooded Twitter since the news broke.

Wishing @PaulDewar a full and speedy recovery after his surgery. And our thoughts are also with your family and many friends. Get well Paul! — Jim Watson (@JimWatsonOttawa) February 17, 2018

Praying for my friend Paul Dewar and his family. He is such a force of integrity and decency. Praying for good health and recovery. — Charlie Angus NDP (@CharlieAngusNDP) February 17, 2018

He’s such a terrific person in every way. “@BCheadle: Devastating news for my old friends Paul, Julia and family. https://t.co/8UEMxl4KFw“ — Elizabeth May (@ElizabethMay) February 17, 2018

My dear friend @PaulDewar is among the kindest, most sincere, and beautiful people to walk among us. With his usual positive energy and conviction, he’s facing a tough challenge. Stand with him. https://t.co/vEamBKDnH6 — Joe Cressy (@joe_cressy) February 17, 2018

Sending my best wishes to @PaulDewar! — Lisa MacLeod (@MacLeodLisa) February 17, 2018

Paul has been a friend, a mentor and an inspiration to me. News that he was going into surgery was hard to hear, but I know no tougher a fighter, surrounded by no more loving and supportive family and friends, than @PaulDewar. He’s got this. All my and @natsbrain‘s love, Paul. — Jeff Leiper (@JLeiper) February 17, 2018

.@PaulDewar was the most incredible politician I’ve ever worked with. Hands down. The ONLY politician I’ve seen attend women’s events & refuse to do media or grab the mic. He’s a good egg. Sending you vibes, Paul! Fuck cancer. 💛 https://t.co/pgnATCGkHm — Julie S. Lalonde (@JulieSLalonde) February 17, 2018

Just wishing my friend @pauldewar the very best…while we disagree on many things…he is one of the good guys…honest decent and thoughtful. Wish him the best and thinking of his family tonight. — John Baird (@Baird) February 17, 2018

Just learned due to remarks posted about Paul Dewar’s brain cancer and surgery @pauldewar. We chatted many times in the House. Wish you and your family all the best and a full recovery. — Wayne Easter (@WayneEaster) February 17, 2018

Oh, I echo that sentiment. Paul, you are a great fighter as was your Mum. You can do this. David and I are pulling for you to recover soon. @PaulDewar https://t.co/QULaDTAieK — penny collenette (@penottawa) February 17, 2018

Dewar was first elected to the House of Commons in 2006. He ultimately lost his seat to Liberal MP and current environment minister Catherine McKenna in the 2015 federal election.

He served as foreign affairs critic and launched a failed leadership bid in 2011.

The former teacher was also notably among the 13 Canadians banned from Russia through retaliatory sanctions in 2014.

Dewar, the son of Marion Dewar, the late former mayor of Ottawa, had been considering run against Jim Watson for the Ottawa mayoralty this year. Nominations for that race open in May.