While ABC prepares for the debut of Christiane Amanpour on This Week, the network says goodbye to another colleague.

Martin Bashir, a co-anchor on Nightline for five years, has announced he is leaving for MSNBC. The British journalist, who has famously done interviews with Princess Diana and Michael Jackson, will front a daily afternoon program on the cable channel. He will also contribute pieces to NBC’s Dateline.

Bill Weir, the current co-anchor of Good Morning America‘s weekend edition, will now share late-night duties Terry Moran and Cynthia McFadden. (Weir’s morning replacement has not yet been announced.)

“Since joining us in 2004, Bill has done some of our most innovative reporting from every conceivable venue, both as co-anchor of weekend GMA and for all of our other programs and platforms,” said ABC News President David Westin.

Bashir will start his new MSNBC post in September. Meanwhile, This Week with Christiane Amanpour will kick off on Sunday Aug. 1.