A little under twelve months on from the John McGinn saga, they have agreed a fee with the Steelmen for the precocious midfield talent.
They dallied around the ex-Hibs star allowing Championship side Aston Villa to nip in and pinch him for the bargain fee of £2.75million. Now he is preparing for the Premier League and worth at least five times that much money.
Peter Lawwell and the Celtic board tested the water with an opening fee for Turnbull, as they are more than entitled to do, but more importantly learned their lesson.
But having been told in no uncertain terms what Motherwell holding out for they came back with an enticing offer - to both the Fir Park side and the player - to make sure he did not end up at a Championship team of much-lesser standing than the Scottish champions.
Not only does it get the player in the door ahead of pre-season, it prevents the frustrating day-to-day speculation which is the transfer window.
There has been reports that another talented player to have left Fir Park for one side of the Old Firm is set to be sent out on loan. Jake Hastie signed a long-term deal with Rangers but manager Steven Gerrard is prepared to allow him to leave temporarily to prevent the player's development from being stunted.
The winger could find an abundance of competition if he stays part of the Rangers first-team next season.
Similarly, Turnbull will be battling for a midfield spot with the likes of Scott Brown, Callum McGregor, Olivier Ntcham, Nir Bitton, Ryan Christie and Tom Rogic, while there is also Ewan Henderson, Youssouf Mulumbu and Eboue Kouassi.
If Celtic had plans to loan the player it would likely have been part of the reported £2.8million - rising to £3.2million - deal they have agreed with Motherwell - the midfielder returning to Fir Park.
Instead, the Steelmen are looking at either Lewis Morgan or Mikey Johnston as a potential loan signing.
It is also hard to make an argument that a 19-year-old with the talent of Turnbull, someone who netted 15 goals in the league the season just past, should be allowed to continue his development elsewhere.
Therefore, it means he will be part of Neil Lennon's plans and, as we stand, likely in direct comparison with Ryan Christie and Tom Rogic for a place.
It is the latter who should be worried.
Despite starting the Scottish Cup final and helping Celtic to the treble treble it has been a difficult and frustrating season for the Australian.
A knee injury picked up on international duty with his national side saw him require knee surgery, prompting him to miss around a dozen games.
In terms of numbers it was his worst campaign since 2014/2015 - which he missed due to a groin problem - recording his fewest appearances and goals.
It is even more frustrating due to the talent Rogic possesses. There are few like him in the league. There are times where he looks like a giant with the finesse of the finest Barcelona pickpockets. He can move at pace with the ball, appearing to be an illusion to opponents.
The player's reliability has always been questioned. Not in terms of what he produces on the field but in terms physically being able to play consistently. That suspicion grows every single time he is removed from a game seemingly around the 60th minute mark.
In the last four seasons he has started 107 games, completing 90 minutes on 40 occasions which equates to being substituted 56 per cent of the time.
There is reason behind it. The attacking midfield position is one which is easy to change during a game, whether it is to freshen up the attack or bringing on a more defensive-minded player to offer more protection.
That being said Turnbull completed the full 90 minutes 23 times last season alone.
Where the bigger worry is on the field. Rogic often delivers in big games with big moments. Against Rangers, against Aberdeen, in cup finals.
It is difficult to pinpoint a defining moment or performance from Rogic during the 18/19 term, while the stats show his influence waned. He was shooting less often, taking players on less often and making fewer penetrative passes than the previous campaign.
He was soon usurped by Ryan Christie who had returned the previous summer from Aberdeen. The Scot offered more dynamism, a vibrancy and willingness to close down without the ball. He was generally more involved in the team's play.
Both Christie and Turnbull are effective as a No.8 and No.10, whereas Rogic talents and qualities aren't suited to a deeper role. He has to be played in the final third where he gets the ball into feet and looks to damage teams.
You can imagine either Christie or Turnbull playing alongside Callum McGregor or Scott Brown more than you can the Australian, especially if Neil Lennon wants to move to a 4-4-2 on occasions.
It would be remiss of Rogic if he wasn't thinking about his future and whether there is enough game time for him at Parkhead next season.
Since arriving back in 2013 and the continued progression he has made with the supreme natural talent there was an expectation at one point that he would be the next player to leave Celtic for mega money.
This summer, with Turnbull poised to arrive, could be the moment that it happens, only slightly more low key, but as graceful an exit as the balletic way he plays football.
If it were to transpire, the new recruit would have huge boots to fill and Rogic would be remembered warmly and fondly. And for all those big moments and stupendous goals.