Striker Derek Riordan has stunned Hibernian supporters by signing a pre-contract agreement with Celtic.
The Scotland international will not be allowed to join the Hoops until January 1, 2007 due to transfer window regulations with his current Hibernian deal ending in October.
The 23-year-old has become a mainstay of the Easter Road success story under manager Tony Mowbray over the last two seasons.
Riordan has scored 43 goals over the last two campaigns for the Edinburgh club.
But the forward has now joined Hibs team-mate Gary Caldwell and Wolves striker Kenny Miller in signing pre-contract agreements with Celtic.
A statement on the club's official website read: 'Celtic are delighted to announce that they have signed Derek Riordan from Hibernian on a pre-contract agreement. The player will join the champions in January.
'Riordan, who has already been capped by Scotland, scored 20 goals for Hibernian this season.
'He becomes manager Gordon Strachan's latest signing for Celtic, following the capture of Scottish internationals Gary Caldwell and Kenny Miller, both of whom will begin their Celtic careers when the players report back for pre-season training.'
The loss of Riordan represents another blow for Mowbray, who has been strongly linked with a return to Middlesbrough to succeed Steve McClaren, who will become England head coach after the World Cup.
Defender Caldwell has already left the club, while striker Garry O'Connor moved to Lokomotiv Moscow earlier this year.
Riordan made his Hibernian debut in the Bank of Scotland Premier League game at Hearts in December 2001.
After a brief loan spell with Cowdenbeath in 2003, where he scored a hat-trick in a 7-5 win over Brechin, the forward became more prominent in the Easter Road first team.
He scored twice in a 3-1 win over Aberdeen in May 2003 to make his mark with then boss Bobby Williamson.
Riordan went on to score 18 goals in the following season before flourishing under new Hibs boss Mowbray, who replaced Plymouth-bound Williamson in 2004.
The Edinburgh-born forward became a first-team regular alongside O'Connor, scoring 23 times in Mowbray's first season.
The youngster made his first Scotland appearance in August 2005 when he replaced new Celtic team-mate Miller in the 2-2 friendly draw in Austria.
But, after rejecting a move to Cardiff later in the month, Riordan was sidelined by Mowbray to allow the player to 'clear his head'.
However, Riordan bounced back to help Hibs clinch a top-six place in the Bank of Scotland Premier League and a second successive Tennent's Scottish Cup semi-final berth, although he was suspended for the defeat by Hearts at Hampden Park last month.