Conor Murray has been named tour captain of the British and Irish Lions in place of the injured Alun Wyn Jones, with the Welsh duo of Josh Navidi and Adam Beard called up to replace Jones and fellow injury casualty Justin Tipuric.
Jones and Tipuric both sustained Tour-ending shoulder injuries during the Lions' 28-10 win over Japan this afternoon.
It had been widely speculated that Ireland captain James Ryan might be called up following the injury to Jones but Gatland has opted to plump for the 25-year-old Ospreys lock Beard, who has made 25 caps since making his debut in 2017.
Murray, who turned 32 in April, is a veteran of two previous Lions tours and is favourite to form a half-back partnership with Dan Biggar for the Test series.
He follows in the footsteps of Paul O'Connell (tour captain in 2009, first test in 2013) and Peter O'Mahony (2017 first test) as recent Lions skippers from Munster.
"We're all incredibly disappointed for Alun Wyn and Justin. The timing of these injuries seem particularly cruel given we fly to South Africa tomorrow, but unfortunately they're part of the game," Gatland said.
"Alun Wyn will obviously be a big loss, both on and off the field, but will be ably replaced by Conor.
"Conor is an outstanding rugby player and is held in the highest regard with both the players and coaches.
"As a three-time Lions tourist, he knows what will be required as captain and I'm certain he will lead the squad with excellence. He will also be well supported by an experienced leadership group.
"We plan for Adam and Josh to join up with the touring party before we depart for South Africa tomorrow evening."