The former Fratton favourite has completed a temporary move to West Brom.
Clarke has indeed joined the former as they prepare for an immediate return to the Premier League under new manager Valerien Ismael.
However, the centre-back has not moved to The Hawthorns on a permanent basis and instead heads out on loan.
He spent the past two years at Derby County and is still to make his Brighton debut after leaving Fratton Park for the Amex in the region of £4m in 2019.
It means that Pompey will not benefit financially as they would likely be due a The Blues had sell-on clauses when they negotiated the sales of Conor Chaplin, Adam Webster and Jamal Lowe.
After joining West Brom, Clarke told the club’s website: ‘I’d like to think I am someone who sets myself high standards and tries to keep to them throughout the whole season.
‘I want to be able to give my best to West Bromwich Albion. I’m really excited by the challenge.
‘As a player, you play football to achieve success.
‘This is a club that is looking to bounce straight back to the Premier League and has had success at this level before.
‘The club knows what it takes to get out of this division and I want to try and help them do it again this year.’
Clarke enjoyed a superb four years at Fratton Park between 2015-2019 following his arrival from Ipswich.
In total, he made 185 appearances, scoring nine goals.
The cultured centre-half was named The News/ Sports Mail Player of the Season for both 2017-18 and 2018-19, while he helped Kenny Jackett's side claim the Checkatrade Trophy in March 2019.
Clarke was named man of the match for his performance in the penalty shootout defeat of Sunderland at Wembley.