Of all the sub-plots when Ireland meet England at Twickenham on Super Saturday, arguably the most tantalising is the battle between Jonathan Sexton and Owen Farrell.
The two number tens have been on two British & Irish Lions tours together, joining forces on the victorious tour Down Under against Australia in 2013 and last year’s tied series in New Zealand.
But while they room-shared in Australia and formed a close bond on the same team together, their professional rivalry in the colours of their countries extends back to the Championships in 2012.
Back then, 20-year-old Farrell was playing in his first Championship and Sexton later revealed in his book that he decided to show him who was boss.
However, after getting the measure of his fellow fly-half and developing a mutual respect on the Lions tour to Australia, Sexton dubbed Farrell an honorary Irishman.
Farrell was also not afraid of showing his admiration for his opposite number after the tour saying: “Johnny is a fantastic player and even though I had respect for him before going, I have even more now.”
While Sexton had been the first-choice No.10 in Australia, with Farrell his back-up, the dynamic had changed by the time the Lions toured New Zealand.
It was now a straight fight between the two for the starting spot – not that Sexton let the rivalry get in the way of his friendship with Farrell.
He described Farrell as “world class” and said that his competition with him for the shirt was probably the greatest in his professional career “because of the respect I have for him”.
They eventually played alongside each other, with Farrell shifting to inside centre to accommodate Sexton.
When it comes to the rivalry between the two in the Championship, though, there is only one winner.
Farrell has started at fly-half three times for England against Sexton, in the 2002, 2013 and 2014 Championships, and emerged victorious on each occasion – twice at Twickenham.
Yet, Ireland have already wrapped up the 2018 Championship with a game to play, with England stuttering to back-to-back defeats to Scotland and France.
England do have the chance to rain on Ireland’s Grand Slam parade, while also getting revenge for their defeat in the reverse fixture in last season’s competition.
The clash on Super Saturday will also see Farrell start at fly-half for the first time since the 2014 Championship, after George Ford was dropped by England head coach Eddie Jones.
With Farrell and Sexton such fierce competitors – not to mention expert tacticians – the latest meeting between the pair is undoubtedly one not to be missed.