As his teenage players gathered before him, Martin Haag had a message. And a request.

And then he asked each of them how they wanted to be remembered after their World Under-20 Championships campaign was over.

Jack Willis thought carefully. And then gave his answer: "The most relentless and versatile back-row forward at under-20 level."

England went on to win that tournament. Four years on, Willis continues to live up to the adjectives he set himself.

This season in the Premiership, he has been a one-man crime wave around the breakdown, burgling ball at an astonishing rate.

In total, he finished with 46 turnovers. No other player reached even 20.

In the modern game, there is no talent more valuable. This season, there has been no better exponent.

Willis could rest on that statistic. He could build a career on it. But in England's congested back row, you have to diversify to thrive.

"I have always focused on attacking the breakdown and the jackal work but I don't want to be a one-trick pony," Willis told Rugby Union Weekly in September.

"I want all areas of my game to be as good as they can be. Having one major skill won't get you very far."

So, as well as the improbably low split-leg stance that has become his calling card at the contest, he has been rampaging in the loose, chopping down ball carriers in defence and soaring in the line-out.

He has been relentless, and has scooped up end-of-season awards like unguarded breakdown ball.

He is the Players' Player of the Year, the Land Rover Discovery of the Season and the Premiership Player of the Season.

England head coach Eddie Jones has doubts about Premiership form as a guide to Test ability. But Willis has been too good to ignore.

This Saturday, as Georgia roll into a empty Twickenham for the first match of the Autumn Nations Cup, he will make his England debut.

It comes at 23. However it has been far from the usual journey from promising youngster to fulfilled potential.

As a boy, Willis played football alongside his rugby. It was while warming up for a kickabout that he first discovered the exceptional flexibility that he has nurtured ever since.

He hit the barre, following his girlfriend's ballet exercises to fine-tune his balance and core strength.

If it sounds outlandish, his teenage CV is equally leftfield.

Some players get on the 'pathway' early. Earning spots on representative teams that put them on the radar of Premiership clubs and England selectors.

Willis had more fundamental concerns. In his early teens, the Reading Abbey team he played for came close to being disbanded because of lack of numbers.

He went for a trial at London Irish - the club his father had played for. And was rejected.

While other prospects chose between scholarship offers from top private schools, Willis had to make his own pitch.

He wrote to The Henley College, a state sixth-form college in Oxfordshire that ran a programme developing players for Wasps, asking for a trial.

That tenacity was clear to Haag as Willis forced his way into England Under-20 squad in 2016.

"He was always pushing to improve, to be the best he could be. He was not afraid to talk up in meetings. If you asked him to present a point to the rest of the team, he could do that," remembers Haag.

"He was part of the banter flying around, but he had a serious head on as well. He was always working hard on his game, doing the extras. He knew it was a great opportunity and he was going to make the most of it."

Joe Marchant, Ollie Thorley and Will Stuart were all part of that group. All are part of this week's senior get-together. All, unlike Willis, have already won their first caps.

Willis could, maybe should, have been before any of them.

After a breakthrough campaign in the Premiership, he was named by Jones in the England squad to tour South Africa in 2018.

But he never made the plane. Instead, he spent the summer mulling over the wreckage of his knee.

As he was carried off and out of the Premiership semi-final against Saracens with extensive ligament damage, he could feel the unsupported joint slipping out of place.

Haag sent him a text of just three words: bigger, faster, stronger.

Willis did eventually return as a more physical, powerful presence, but also as a more rounded person.

As he fixed his knee, he also learned to fix radiators and taps, taking a plumbing course during his down time.

He started a property business, hunting out potential investments for others.

"Rugby had become a bit of a bubble - it was all I thought and spoke about 24 hours a day to family and friends," added Willis.

"Everything that was going on was rugby. When I got the injury and that was taken away, you realise there is a lot more around you."

Versatile. Relentless. In four years, plenty has changed. But some things haven't.