Featuring the Nissan X-Trail seven-seater, the company tweeted a picture of the interior of the vehicle with a crown on each seat.
The ad carries the words, "It could be triplets and there would *still* be enough room for the Queen," and the hashtags #XTrail #SevenSeats #RoyalBaby.
The birth of soon-to-be older brother Prince George in July 2013 led to a slew of tactical ads from brands including Coca-Cola, Warburtons. Airline Ryanair also temporarily renamed itself Ryanheir.
Brands such as Marks & Spencer, Tesco and Jack Wills have been among the first to congratulate the Duke and Duchess of Cambridge on their news via Twitter.