The meeting, in Mr Cook's rooms at Westminster, marks a truce in one of the longest-running private wars in British politics. Labour's two big-hitters have been at loggerheads for almost 20 years.
The summit also exposes a move by the Cabinet to close ranks round the Foreign Secretary as the Conservatives gear up for a critical Commons debate this week on his turbulent private life and his fitness for high office.
The Chancellor is understood to have told him: "These things are temporary. It will go away." But the Opposition plans a further onslaught in Wednesday's debate and through a series of parliamentary questions.
The Tories scent blood, but the party's high command has decided on a "measured" attack, rather than a crude demand for Mr Cook's resignation.
The Chancellor urged the Foreign Secretary at their private meeting on Thursday night: "I am here if you need me. We may have had differences in the past, but this is the sort of thing that brings a government together."
Their candid get-together indicates that ministers fear that Mr Cook has been seriously damaged by the steady drip, drip of embarrassing revelations, culminating in last week's disclosure that he sacked his Foreign Office diary secretary, Ann Bullen, and tried to hire his mistress and Commons secretary, Gaynor Regan, in her place.
Mr Brown and Mr Cook coveted the key post of Chancellor in Labour's first government for two decades.
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