Former Labour leader Neil Kinnock has said Robin Cook would have returned to the Cabinet had he lived.
Robin Cook's relations with Gordon Brown had improved
Mr Cook, who died on Saturday, resigned from the Cabinet on the eve of the Iraq war but Lord Kinnock said he would have been invited back as time passed.
"Robin was so good that it was unwise to do without him," he told BBC News.
Cabinet minister David Blunkett also said Mr Cook could have played a part, even under Tony Blair, as the "wounds" from the Iraq debate healed.
There has been speculation that Mr Cook could have rejoined the government if Gordon Brown took over the premiership.
Lord Kinnock said neither Mr Cook nor Mr Brown could remember the origins of the feud between them which emerged when they were young men in Edinburgh.
But their relationship had recently been better than ever, he said.
"Their relationship was much warmer and mutually admiring than it had been for some decades, he said.
He predicted Mr Cook would have been invited back to Labour's front bench regardless of who was leader as the event, though not the implications, of the Iraq war receded.
"I am certain that such was the capability of Robin Cook and so sure-footed had been his whole conduct in the period since he had left the government that he would have been invited back to the front bench.
"And depending on the post, I think he would have been strongly inclined to commit himself again."
Lord Kinnock said Mr Cook would not have worried about "pecking orders" but would have assessed how much he could achieve in a particular job.
Mr Cook managed Lord Kinnock's campaign for the Labour leadership in 1983.
The Labour peer said he felt an awful sense of injustice at the loss of a "cherished friend and true comrade".
"Robin had so much more to give, so much more to do and much more to enjoy," he said.
He paid tribute to Mr Cook's "overwhelming intellect" but said he could also be "very, very funny" with his dry humour.
Politically, the former foreign secretary had been totally consistent with his basic beliefs, said Lord Kinnock, who revealed he had tried to dissuade his friend from resigning over the Iraq war.