Ange Postecoglou's Celtic won the Scottish Premiership title this season with a little help from the Three 'R's.

Rotation, resilience and relentlessness.

However, there was actually a fourth 'R' lurking in the shadows; Ruthlessness.

It has been the hallmark of a 31 game unbeaten league run that has driven the Hoops to title glory this term.

We Never Stop and all that.

On Wednesday night Postecoglou completed phase one of the rebuilding of his beautiful house as Celtic gained the point required at Tannadice against Dundee United to seal the title deal.

At long last Postecoglou had ticked off a lifelong managerial football ambition by winning a league title with a world-famous European club.

His ambitions for Celtic know no bounds.

It is this sort of ruthlessness that drives, determines and defines the Aussie.

A ruthlessness which saw phase two of the rebuild take shape in the form of some bombshell news for the Celtic faithful.

The Celtic supporters had barely time to drink their morning Friday coffee when it filtered through that Tom Rogic and Nir Bitton's Celtic career was over after 10 trophy-laden years.

For many fans, this was not a Good Friday.

The two heroes in Hoops will bid their fond farewells inside Paradise during Saturday’s Trophy Day presentation when Postecoglou's team take on Motherwell.

The duo have been at Parkhead for over nine years and amassed 34 trophy wins between them.

Australian internationalist Rogic signed from Central Coast Mariners during the January window of 2013.

He had just turned 20 and made his Celtic debut a month later.

Rogic played 271 games during which he netted 46 goals - all, or nearly all, things of beauty - while picking up no fewer than six championship medals, five Scottish Cups and five League Cups to take his medal haul to a highly respectable 16.

Israeli internationalist, Bitton joined in the summer of the same year from FC Ashdod and he made his debut in the San Siro against AC Milan in the UEFA Champions League in September.

Bitton turned out 269 times and scored 14 goals.

He picked up eight title medals, four Scottish Cups and six League Cups taking him to a medal tally of 18.

READ MORE: Nir Bitton makes Celtic 'domination' claim as Parkhead hero thanks 'amazing' fans for support

Publicly, Postecoglou dished out the plaudits to two wonderful servants to the men in green and white.

The 56-year-old said: “While we are very sad to see both Tom and Nir leave the club, we totally respect their decisions in wanting to seek a different challenge in football, having both played their part in our success for the past decade.

“They have certainly made such a tremendous contribution to Celtic over such a long and successful period for the club and I understand that in their minds the time is right to move on."

Privately the mood music may be different.

Both men still had a year to run on their deals but unlike 30-year-old James Forrest, there was no extension or three-year deal in the pipeline for Rogic or Bitton.

Some of the Celtic supporters were critical of the club offering Forrest such a deal.

The deal makes sense more now in light of the experience to be shed as Celtic sever ties with such a trophy bedecked duo.

There still has to be a smattering of players who have been there, seen it, done it and got the T-shirt so to speak.

His experience, knowledge and wisdom will be even more vital to the Celtic cause moving forward.

The winger still has a lot to offer when he is fully fit.

Whilst Bitton's exit is easier to fathom and stomach - he had become the club's ultimate utility player - but the Israeli thrived and prospered under Postecoglou.

That was in large part was down to the Aussie's man-management skills and ability to get a tune out of all of his squad.

It had become something of a standing joke that there were three certainties in life - death, taxes and Nir Bitton playing at centre-back in the Champions League qualifiers.

That tactic was usually the bat signal of a club in distress and being ill-prepared to go into European football's premier club tournament.

More often than not it ended in tears at the qualifying stage.

How ironic in a season where Celtic have entered the lucrative Champions League group stages proper that the very definition of the club's go-to guy in a defensive sense will be nowhere to be seen.

It feels like a changing of the guard.

Celtic are tooling up for an assault on the Champions League.

A serious assault.

This is why the decision to cut loose Rogic despite having 12 months to run on his present deal may well raise eyebrows but it feels right at this juncture.

He has performed to the highest standard for his compatriot and he has arguably produced the best football of his Celtic career outwith a spell under Brendan Rodgers.

The Aussie is a mercurial talent.

He is capable of producing spell-binding moments of magic in matches but the Wizard of Oz can also magically disappear in games.

You can produce an outrageous DVD of Rogic's most spectacular moments and goals in a Celtic shirt.

It would be a sublime film.

It would be a fantastic montage where Rogic's skills elevated himself as well as Celtic out of the ordinary.

The Invincible Scottish Cup final goal in 2017 is a case in point.

Celtic Way:

The curler at Ibrox in the 3-2 game in 2018 is another.

There is a litany.

The fleet-footed star has produced these wonderful and incredible moments during his nine-year Celtic career.

He played football beautifully at times, the sporting equivalent of poetry in motion.

It is also fair to say that those moments have been fleeting a bit like his performances on the European stage too.

Had Rogic left to go to Qatar last season after the 10-in-a-row bid had collapsed then not many Celtic supporters would have batted an eyelid.

This is a player who after all has played in less than half the available games Celtic have had.

He has to my knowledge missed over 100 games for the club that he could have featured in.

This season he will have played the most minutes of any campaign in his stay at the club.

Again it was Postecoglou who resurrected Rogic and allowed him and inspired him to prove his worth again - yet he's also the one who's sanctioned his departure.

As you'd expect from a frequently injured player, he can sometimes take time to get back up to speed.

Heading, tackling and tracking back has never been Rogic's forte either.

Postecoglou may feel that the Aussie is not the man to give Celtic intensity and physical presence in the engine room moving forward.

Celtic are lacking in midfield areas that are not Rogic's strengths.

Discussions will have taken place on whether or not to offer Rogic or Bitton new deals.

Whilst there was may have been a reluctance in Postecoglou to let both players go the long and short of it is the duo were not offered new deals by Celtic and now see their respective futures lying elsewhere.

Sometimes decisions have to be made that are unpopular.

So Rogic (and Bitton) being jettisoned from Celtic may well serve as one of those decisions.

As a business conclusion, it makes perfect sense for the players to be moved on now despite both having 12 months left to run.

All things have a natural beginning and end.

It's the end of the green and white brick road for the Wizard of Oz.

READ MORE: Matt O'Riley reveals Celtic transfer change of heart as he charts League One to title winner journey

Both players were fine servants for Celtic and it is perhaps fitting that they leave the club as champions.

The manager has not got much wrong since he planted his feet on Scottish soil last June.

Postecoglou certainly means business. He desperately wants to make an impact on the greatest club tournament on earth.

For once Celtic could be about to embark on the Champions League group stages in the strongest possible shape and prepared.

For once Celtic appear to be treating the competition with the respect and the reverence it deserves.

Due to his domestic exploits this season the Aussie has earned a crack at the big tournament and should expect the full backing of the board.

After all, Postecoglou has serious designs on turning Celtic into a major European football force once again.

In order to do that he is going to have to be ruthless.

Bitton and Rogic will not be alone in terms of players heading out the Parkhead exit door in the summer.

More players will also arrive as Postecoglou puts his extensive knowledge of world markets as well as his own keen eye for identifying talent to good use whilst attempting to fashion a side that is Champions League ready and fiercely competitive.

The manager won't be satisfied until he has taken Celtic to the next level.

As midfielder Matt O'Riley said in the aftermath of Tannadice: "I don't just want to play in the Champions League, I want to win games."

Those words could well have been Postecoglou talking himself.

It is all part of a long-term strategy and masterplan for Celtic.

Celtic has entered a new era.

Phase two of the rebuild starts now.