Arsenal have signed defender Kieran Tierney from Celtic on a long-term deal.
The Scotland international, 22, has joined from the Scottish champions for a fee of £25million.
The left-back, who will wear the number three shirt, passed a medical in London on Thursday and could make his debut against Newcastle on Sunday.
Manager Unai Emery said: "We're delighted Kieran is joining us. He's a very talented player who will continue to improve.
"He increases our options defensively and I look forward to him joining our group."
Tierney, who has won 12 caps for Scotland, made over 150 appearances for Celtic after making his debut in 2014.
He becomes the club's fifth summer signing following the arrivals of Nicolas Pepe, Dani Ceballos, William Saliba and Gabriel Martinelli.
The Gunners are hoping that is not the end of their business as they try and finalise a deal for Chelsea defender David Luiz.
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Arsenal will face Ostersund and their English manager Graham Potter in the last 32 of the Europa League.
Monday's draw paired Arsene Wenger's men with the Swedish side, who former York defender Potter has taken from the fourth division to the top-ranked Allsvenskan in six years.
The 42-year-old has earned comparisons with Roy Hodgson - who himself managed in Scandinavia in his formative years - and this will be his first clash against English opposition.
The draw also saw Celtic come out against Zenit St Petersburg.
Kolo Toure has taken up a coaching role at Celtic. The 36-year-old has been handed the title of technical assistant, with the club stating he would be "supporting on all first-team coaching matters, as well as using his knowledge, experience and expertise to assist across the club's various youth levels".
The former Arsenal and Liverpool defender made 17 appearances for Celtic after being reunited with former Anfield boss Brendan Rodgers last summer, and had been hoping to extend his playing career.
Quoted on the club's official website, Toure said: "I couldn't be happier to be back at this great club.
"This is a new chapter in my career, a new beginning. The football is over now. I can officially say I am retired from playing and now I am fully concentrating on coaching.
"For me there is no big change in terms of what I will be doing. I have always been the kind of player who tries to help those around me.
"Now I will try to give advice, help the young players and just guide them and pass on all the experience I have acquired during my career."
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Celtic have been fined 19,000 euros (£16,051) by UEFA owing to the conduct of some of their fans during the Champions League defeat at Manchester City in December.
The governing body announced the sanctions on Friday morning, saying the charges were related to the setting-off of fireworks in the away end at the Etihad Stadium.
Celtic drew the December 6 clash 1-1 but failed to qualify from the group they shared with City, Barcelona and Borussia Monchengladbach.
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Celtic winger Scott Sinclair has no fears ahead of the visit of Barcelona as he looks for major improvement on their Nou Camp showing.
Brendan Rodgers' team suffered their heaviest European defeat when they lost 7-0 to the Catalan side in September.
But Sinclair was heartened by Celtic's progress between their double header against Borussia Monchengladbach, when they drew 1-1 in Germany following a 2-0 home loss.
And he believes they can make significantly greater advances when they try to get off the bottom of their Champions League group at Parkhead on Wednesday.
The former Swansea, Manchester City and Aston Villa player said:
We have learned a lot and everyone will just be looking forward to that game, including the fans,"It's a massive game for us to prove ourselves.
There's no apprehension. We've learned a lot from that game. Even when we went away to Monchengladbach we showed the difference when we conceded. We lost the game at home, but we went there and drew. I think we've learned a lot and hopefully now we're going in with a positive mindset.
Manchester City beat Barcelona, so anything can happen and it's very different when you're playing at home. Being in front of our own crowd will spur us on because those fans are unbelievable. Barcelona have been beaten here before, so, hopefully, we'll do it again.
Celtic have been fined 10,000 euros (£8,616) by Uefa after fans displayed an "illicit banner" during their recent Champions League qualifier against Hapoel Be'er Sheva.
Fans flew Palestine flags before and during the match against Israeli opposition at Parkhead on August 17, drawing a charge from European football's governing body.
Uefa viewed the flags as illicit banners under article 16 of its disciplinary regulations and at a disciplinary hearing the complaint against the Scottish champions was upheld and the club was fined.
The Uefa rule in question forbids the use of ''gestures, words, objects or any other means to transmit any message that is not fit for a sports event, particularly messages that are of a political, ideological, religious, offensive or provocative nature''.
Celtic have been punished eight times in five seasons by Uefa for supporter misconduct and the sanction on each occasion has been a fine from the governing body.
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