THORNE gained further first-team experience at Portsmouth last season - during two loan spells with the South-Coast club.
The 6ft2in midfielder made 14 appearances for Pompey who were relegated to League One following an automatic ten-point deduction for entering administration in February.
Thorne also made six appearances for Albion last term, including a memorable 3-2 victory away at Newcastle.
Thorne signed his first pro contract on The Hawthorns pitch before kick-off of Albion's Coca-Cola Championship game with Nottingham Forest on January 8, 2010.
He twice signed new contracts in the summer after establishing himself as a fully-fledged first-team player.
His latest deal saw him pen a new-and-improved three-year deal, plus a further year's option in the club's favour.
Academy product Thorne made his Barclays Premier League debut as a second-half substitute in the final game of the 2010/11 season at Newcastle.
But he was pulled out of the England squad for the Under-20s World Cup by Roy Hodgson in the summer to spend the whole of pre-season training and playing with the first team.
Thorne became Albion's youngest league debutant in 49 years when he came on as an 88th-minute substitute in the Baggies' 4-0 Coca-Cola Championship win at Sheffield Wednesday on Saturday, November 28, 2009.
He was 109 days older than Bobby Hope when the Scot made his debut against Arsenal in April 1960, aged 16 years and 219 days.
He was also part of England Under-17s 2010 European Championships-winning squad.
Thorne joined the club at Under-16s level and broke into the Baggies' reserves side three sasons ago.
He was part of the England Under-16s side that won the Victory Shield in December 2008 and the prestigious Montaigu tournament in France, in April 2009.
(LAST UPDATED AUGUST 15, 2012)