Twitter is finally buying TweetDeck for more than $40 million in cash and stocks. TweetDeck is a third-party client for the Twitter and It is the most popular Twitter application with a 19% market share as of June 2009, following only the official Twitter.com website with 45.70% share for posting new status updates. 

The purchase isn't official yet and neither of the company has publically spoken about this deal.

On Monday night Twitter's PR employee tweeted For all those who might be curious, we continue to not comment on rumors.

Last month, the Wall Street Journal reported that Twitter might buy TweetDeck.

A few months ago there was a report that UberMedia, the top developer of apps and Web-based services for Twitter users and other social media platforms, was in chat to acquire Tweetdeck. However, the deal didn't go through.

Twitter has known to either downplay third-party apps or purchase them outright.

TweetDeck would be an important tool for either service, as it's now one of the most popular clients.