Sigurdsson completed a club-record £45 million move to Everton on Wednesday.
Gylfi Sigurdsson's affiliation with Everton began as long ago as 16 years - a man purporting to be the new Toffees recruit's brother has claimed on Twitter.
Sigurdsson completed a club-record £45 million move from Swansea on Wednesday, having been pursued by Everton for much of the summer.
But according to @OliMarSig on Twitter, Sigurdsson first represented the Merseyside club at a 2001 tournament in Germany.
Alongside two images of the Iceland international - one taken on Tuesday and another as a youngster, beside the statue of Everton legend Dixie Dean - he wrote: "Back in blue".
And in a separate tweet, he added: "(Sigurdsson) trained for a week with Everton, got to be a ball boy at Goodison and later went with Everton to Germany for a tournament.
"Once a blue..."
Trained for a week with Everton, got to be a ball boy at Goodison and later went with Everton to Germany for a tournament. Once a blue...— Ólafur Már Sigurðs (@OliMarSig) 16 August 2017
Though nothing came of Sigurdsson's early Everton experience, he returned to England four years later and signed for Reading on an academy scholarship.
After progressing through the Royals' ranks, the now 27-year-old later played for Hoffenheim, Swansea City and Tottenham Hotspur, from whom the Welsh side re-acquired him in 2014.
Gylfi Sigurdsson in action for Swansea City
In total, Sigurdsson has appeared 182 times in England's Premier League, scoring 42 goals and providing 34 assists.