From ESPN.com:
The Dallas Mavericks have agreed to a trade with the New York Knicks for All-Star forward Kristaps Porzingis, league sources told ESPN’s Adrian Wojnarowski on Thursday.
The trade also includes the Knicks sending Courtney Lee and Tim Hardaway Jr. to the Mavericks in return for Wesley Matthews, Dennis Smith Jr. and DeAndre Jordan, league sources told Wojnarowski. The deal may also include draft assets, sources said.
The Mavs are working to acquire a first-round pick to include in the deal, sources told ESPN’s Tim MacMahon. They owe their own protected first-rounder to the Atlanta Hawks as part of the draft-night trade to acquire Luka Doncic.
Jordan and Matthews both have expiring contracts.
Somehow, the Knicks will continue their insane streak of not resigning any rookie that they have drafted since Charlie Ward. We all know that Frank will be next in that little streak, right?
Meet the new boss, same as the old boss.
EDITED TO ADD: While I am not a fan of the trade, the Knicks did also get two future first round picks from the Mavericks in the deal. It appears that it will be an unprotected 2021 pick and a 1-10 protected 2023 pick.
[Sports Illustrated] 
[FOXsports] 
[NYTimes]