Athos had invented the phrase, family affair.

A family affair was not subject to the investigation of the cardinal; a family affair concerned nobody.

People might employ themselves in a family affair before all the world.

Therefore Athos had invented the phrase, family affair.
Aramis had discovered the idea, the lackeys.
Porthos had discovered the means, the diamond.
D'Artagnan alone had discovered nothing--he, ordinarily the most inventive of the four; but it must be also said that the very name of Milady paralyzed him.
Ah! no, we were mistaken; he had discovered a purchaser for his diamond.
The breakfast at M.de Treville's was as gay and cheerful as possible.
D'Artagnan already wore his uniform--for being nearly of the same size as Aramis, and as Aramis was so liberally paid by the publisher who purchased his poem as to allow him to buy everything double, he sold his friend a complete outfit.
D'Artagnan would have been at the height of his wishes if he had not constantly seen Milady like a dark cloud hovering in the horizon.
After breakfast, it was agreed that they should meet again in the evening at Athos's lodging, and there finish their plans.
D'Artagnan passed the day in exhibiting his Musketeer's uniform in every street of the camp.
In the evening, at the appointed hour, the four friends met.

There only remained three things to decide--what they should write to Milady's brother; what they should write to the clever person at Tours; and which should be the lackeys to carry the letters.
Everyone offered his own.