Shane Duffy has made a season-long loan move to Scottish Premiership champions Celtic on undisclosed terms and subject to international clearance.
The Irish international heads to Glasgow after four years with Albion, following his move from Blackburn Rovers in 2016.
He moves to Parkhead with the aim of helping Celtic secure an unprecedented tenth successive league title.
Head coach Graham Potter said, “Shane is part of Albion history. He has been a big part of the club’s recent progress in winning promotion to the Premier League and in retaining our place in the top-flight.
“He is keen to play regularly and, with increased competition in the centre of defence, we cannot guarantee that. This move is a huge opportunity for Shane and on behalf of everyone at the club we wish him well for the season.
“From a personal point of view he has been an absolute pleasure to work with, and as a man and a character he is someone we all love.
“This has been a challenging year for him on and, more importantly, off the pitch, but I’m grateful for the opportunity I’ve had to work with Shane and develop the relationship I have with him.”
Duffy became the club’s record signing in 2016 and in his first season he helped the club secure automatic promotion to the Premier League - forging a formidable partnership alongside Lewis Dunk in central defence.
That partnership served Albion well in the Premier League over the past three seasons and Duffy won the club's Player of the Season award in 2018/19.
The 28-year-old defender - who began his career at Everton and has been capped 33 times by Republic of Ireland - played more than 100 games for Albion, scoring eight goals.
His current contract with Albion, signed in 2018, has three years left to run.