Peter Hain MP - whose family fled South Africa because of its support for Nelson Mandela - has led tributes to the country's former president, who has died age 95.
The Neath MP described him as a "friend and hero" and the "icon of all icons".
The National Assembly's flags will fly at half mast on Friday and again on the day of Mr Mandela's funeral.
First Minister Carwyn Jones said Mr Mandela was one of the "greatest figures of modern times".
Mr Mandela had been receiving intense home-based medical care for a lung infection after three months in hospital.
In a statement on South African national TV, South African president Jacob Zuma said Mr Mandela had "departed" and was at peace.
"Our nation has lost its greatest son," Mr Zuma said.
Following the news, Mr Hain led tributes to the Noble peace prize winner.
Mr Hain said there had long been a bond between Wales and the man known to friends as "Madiba".
He cited the anti-apartheid demonstrations against the then all-white Springboks rugby team's game in Swansea in 1969.
The former Welsh Secretary also fondly recalled Mr Mandela's first and only visit to Wales in 1998, when he was awarded the Freedom of Cardiff.
He said: "Cardiff that day experienced a vintage Mandela performance.
"He ignored my guiding arm on his elbow and stopped at a group of primary school children sparkling in Welsh national dress.
"As the queue of VIPs waited, sweating in the unusually hot weather, he began conducting the children to Twinkle, Twinkle Little Star.
"I later learned that it was the absence of his children that he missed most in all his long years of imprisonment on Robben Island."
Mr Hain, whose family's associations with the anti-Apartheid movement saw them blacklisted by the South African authorities in the 1960s, also described Mr Mandela as "a friend and a hero".
Recalling Mr Mandela's 2000 visit to the Labour Party conference in Brighton, he said: "As I escorted him inside, he asked his usual question: 'How's the family?'.
"On hearing my mother was in Swansea's Morriston Hospital with a fractured femur, he stopped immediately and said that he must speak to her.
"Out came my mobile and, when she answered from her hospital ward, she was greeted with: 'Hullo. Nelson Mandela here, do you remember me?'
"That's what made him so extraordinary - he remained above all a people's person which is highly unusual amongst global leaders or celebrities of his stature."
First Minister Carwyn Jones led tributes from the Welsh Assembly.
He said: "Nelson Mandela can be truly described as one of the greatest figures of modern times.
"Not many people can claim to have changed the history of their nation for the better, by bringing together what was then a bitterly divided society.
"His message of forgiveness, of reconciliation for the sake of a better future is one all of us should follow."
He added: "When President Mandela visited Wales in 1998, he thanked the Welsh people for their support - it was a moment we will never forget.
"But for all that we did, we didn't have to confront apartheid on a daily basis.
"We didn't have to run the risk of imprisonment or worse.
"Nelson Mandela faced his struggle with dignity and without bitterness and that is why he will be remembered for generations to come."
Leader of the Welsh Conservatives, Andrew RT Davies AM, said: "Nelson Mandela was - and will always be - a global inspiration.
"His was a life that has defined what it means to be truly great."
Leanne Wood, Plaid Cymru leader, said the world would mourn "a great man who has inspired generations and whose achievements will last forever".
Kirsty Williams, leader of the Welsh Liberal Democrats, said Mr Mandela's "ability to unify communities and deliver justice to a fractured and tormented state are unparalleled and his legacy will continue for generations to come".
The assembly's presiding officer, Rosemary Butler, said flags would fly at half mast on Friday and on the day of Mr Mandela's funeral.
She said: "These days we often apply the description 'great' to people but Nelson Mandela truly was a great human being."