Very sad news. Tim Russert has died of a heart attack, at 58. News started spreading within the last half hour through media and political circles. It's now been confirmed by The New York Times.

Our deepest condolences to his family, friends and colleagues.

Late Update: Video of Tom Brokaw announcing Russert's death on MSNBC this afternoon. Brian Williams was on location in Afghanistan and joined the newscast later.

Later Update: Russert's final online chat at MSNBC.com, from earlier today.

Later Still: NBC's Chuck Todd reminisces about Russert: