Media playback is unsupported on your device Media caption Steffan Lewis with his family while being sworn into the assembly in 2016

One of Wales' youngest assembly members has died at the age of 34.

Steffan Lewis, the Plaid Cymru AM for South Wales East, was diagnosed with terminal bowel cancer in late 2017.

Plaid leader Adam Price said the party was in a state of shock at losing its "brightest star", while tributes were paid across the political divides.

Mr Lewis, who was brought up in Crosskeys and Tredegar in the Gwent valleys, leaves wife Shona and three-year-old son, Celyn.

"He was our rock, he was our anchor and most certainly, our hero. To lose Steff is the greatest possible blow to our family," his family said.

Plaid Cymru said he passed away quietly in Ysbyty Ystrad Fawr, in Ystrad Mynach, on Friday.

First Minister Mark Drakeford said he was one of the "most decent and able politicians of his generation". Flags have been lowered at the National Assembly in Cardiff Bay as a mark of respect.

Mr Lewis' family said: "Steff inspired us every day.

"Steff fought this disease with the same courage and determination that he applied to his politics, and even when he was in great pain and discomfort, he continued to serve the people he so dearly loved to represent.

"We know that there are people throughout Wales who share our sense of loss."

Image copyright Plaid Cymru Image caption Steffan Lewis had been an Assembly Member for the South Wales East region since 2016

His family said they will ensure "his legacy will live on forever - in our community, in our hearts and above all through his son".

"Wales will not forget his contribution and his determination to make a difference to people's lives," they added.

The AM was elected to the Welsh Assembly in 2016, having previously served as former Plaid Cymru leader Leanne Wood's speech writer.

It was in his work on Brexit, in his capacity as the party's spokesman on the subject, where he had his biggest impact.

Image copyright Plaid Cymru Image caption Steffan Lewis addressed the 1997 Plaid Cymru conference in Aberystwyth

The young AM had a major role in the joint Labour-Plaid policy on leaving the EU, published at the beginning of 2017.

Later, his proposal for an Act to enshrine EU rules into Welsh law was employed by the Welsh Government as a tactic in its negotiations with the UK government.

His illness did not stop him from making contributions to Senedd debates, and AMs from across the parties rallied around him after he was diagnosed - taking part in a charity walk organised by Mr Lewis's sister, Nia.

He spoke about the emotional toll of living with cancer in interviews, saying he had learned it was "OK to be frightened".

Plaid leader Mr Price said: "Steffan first addressed a Plaid Cymru conference at the age of 14. It was clear at that point that this was somebody that was going to have a big impact on the life of the nation.

"He will be remembered as a politician of rare talent who achieved an incredible amount during his time in elected office, which has been cut short in such harrowing circumstances."

Image caption Steffan Lewis was one of the "most decent and able politicians of his generation", Mark Drakeford said

A book of condolence has been opened in the Senedd for colleagues and members of the public to leave tributes.

Elin Jones, the assembly's presiding officer and a Plaid Cymru AM, said: "Steffan showed great dedication and courage in continuing to serve the people of South Wales East throughout his difficult illness.

"His determination to serve and work hard to improve the lives of the people of Wales earned him respect from across the political divide, within the Senedd and further afield.

"I cannot recall another AM who was as proud as Steffan to have been elected to his national parliament. That his term of office was cut so short is a tragic loss for us all."

Welsh Secretary Alun Cairns said: "He was exceptionally bright and hugely talented. Wales has lost a first rate politician and public servant."

Welsh Conservative leader Paul Davies said: "His courage and his bravery throughout his illness will be an example to us all."

Rhun ap Iorwerth, a fellow Plaid AM, called Mr Lewis "a young gentleman of immense political ability".

Scottish First Minister Nicola Sturgeon said she was lucky to know Mr Lewis, adding: "He was a truly lovely man and a first rate politician."

Labour AM Dawn Bowden said it was a "very dark day", while former First Minister Carwyn Jones said Mr Lewis was "admired across the parties."

UKIP assembly leader Gareth Bennett said: "While our politics may have differed, nobody can doubt Steffan's commitment to what he truly believed in, nor his gifted oratory. Our politics will be the poorer without him."

Education minister and Liberal Democrat AM Kirsty Williams said: "When he addressed the chamber you listened because you knew he always had something thoughtful to say."

She said he was "exactly the kind of person the assembly needs".

Welsh Liberal Democrat leader Jane Dodds added: "Steffan was a talented and committed assembly member.

"He was popular and respected across political parties and he had a bright future ahead of him. It's tragic he's gone so young."