At a news conference in Brussels, Belgium this morning, Daimler AG and the Renault-Nissan alliance officially announced that the three automakers would collaborate on future products and that each would exchange shares in the other companies. The deal has been rumored for months, and Daimler has been looking for a partner to help spread the costs of small car development for years.

Under the new agreement, Daimler will hold a 3.1-percent stake in Renault and Nissan and the existing alliance partners will hold an identical stake in the German company. The partners will develop a combined platform that will be used as the basis for the next generations of the Renault Twingo and Smart cars, including a new four-seater. These new models will launch in 2013 and the current Smart factory in France will continue building the two-seat version. The new four-seater, along with the Twingo, will be built at a Renault factory in Slovenia. All three vehicles will be available from launch in gas, diesel and electric drive variants.

The automakers will also share powertrains for other models. Renault-Nissan will provide small gas and diesel engines to Daimler for use in its smaller cars, including presumably the next generation A, B and perhaps even C-Class Mercedes-Benz models. Going the other way, Daimler will provide some of its engines to Nissan for use in Infiniti models. The partners will also collaborate on light commercial vehicles, with Renault providing a new entry-level van to be sold as a Mercedes.

[Sources: Renault, Daimler]

We've all been wondering exactly what flavor of fruit the Daimler AG/Renault-Nissan mash-up would bear, and now it looks like we may have our first answer. Starting soon, the Infiniti G will boast an efficient four-cylinder engine borrowed straight from Mercedes-Benz. AutoWeek reports that Nissan head-honcho Carlos Ghosn confirmed the news himself, though so far we have no indication of exactly which four-pot will make its way into the Japanese sedan or when it will be available to buyers.

The suits at both Infiniti and Mercedes-Benz don't seem to be too concerned about the new four-cylinder G robbing sales from the Silver Arrow. Ghosn said that customers typically don't cross-shop the two brands at all. Instead, Infiniti will benefit from having a new efficient option for buyers that will help the company meet impending fuel standards, and Mercedes-Benz will move more powerplants than before. Win, win.