Who Is Billy Gilmour?  (Sky Sports)

Chelsea have signed Rangers' highly-rated 15-year-old Billy Gilmour, but who is the Scottish youngster?

The Blues won the race to sign the midfielder, who is regarded as one of the brightest young prospects in Scottish football, and, according to Sky sources, will pay a £500,000 development fee to Rangers with additional payments due on the attainment of specific career milestones.

Rangers boss Pedro Caixinha did his best to persuade Gilmour to stay at Ibrox, holding talks with his parents in a bid to convince him to snub the advances of Chelsea, but the youngster has decided to take his chance with the English champions-elect.

So here's all you need to know about the 15-year-old wonderkid...

Time at Rangers

Born in Ayrshire on June 11, 2001, he joined Rangers as a young boy and quickly progressed through the club's academy.

He made his debut for Rangers' U20 side in December and has risen to prominence this season after a series of excellent displays for Graeme Murty's development side.

His performances saw him promoted to training with the first team and he was also given a squad number.

Murty, who took temporary charge of the first team following the departure of Mark Warburton, was impressed and revealed Gilmour was even close to making Rangers' matchday squads for their Scottish Cup ties against Morton and Hamilton.

Speaking at the time, Murty said: "Billy was really, really close to being in the squad. He has played really well for the 20s.

"He has done really well for me when he has played for the 20s, so the next logical step is the first-team, and it's just a question of as and when we can dip him in that's appropriate to him. But, it was really close and a hard decision for us to make. But, I wanted him to get on the pitch and experience the atmosphere."

Scotland youth international

Gilmour has also impressed at youth level for Scotland.

He was one of the standout performers for Scotland as they finished second to Republic of Ireland in the 2016 Victory Shield.

Celtic youngster Karamoko Dembele grabbed most of the headlines after appearing for the Scots during the tournament as a 13-year-old but it was Gilmour who caught the eye with his performances in midfield, alerting a number of scouts at the top European clubs to his talents.

Earlier this year he captained Scotland's U16 side to glory in the four-way UEFA Development Tournament against Croatia, Iceland and Austria and was named in Scotland's provisional squad for the UEFA European U17 Championships.

Who was interested?

The list of clubs reportedly interested in Gilmour reads as a bit of a who's who of European football.

Chelsea, Manchester United, Manchester City, Arsenal, Real Madrid and Barcelona were all keeping tabs on the 15-year-old after his displays in last year's Victory Shield.

Rangers even admitted as much in their statement which revealed the midfielder was joining Chelsea.

The statement read: "That he was sought after by many Premiership clubs, and indeed a number of the largest clubs in Europe, further demonstrates the quality of player now being produced by the Academy."

Why Chelsea?

Rangers did all they could to try to keep Gilmour at Ibrox.

But reports suggest a visit to Chelsea's Cobham training ground convinced Gilmour to move south and join Antonio Conte's Premier League champions-elect.

He will move to Stamford Bridge in the summer when he turns 16 and is expected to be part of the Blues' academy, which just won the FA Youth Cup for the fourth year in a row.