Even prior to them becoming rivals for the Ireland number ten shirt, there was real animosity between Ronan O'Gara and Johnny Sexton.
Their rivalry for the shirt would start in the autumn of 2009 with Sexton's Ireland debut and end in 2013 with O'Gara's international retirement.
Speaking on Jarlath Regan's 'An Irishman Abroad' podcast, O'Gara opened up regarding his relationship with Johnny Sexton.
My relationship with Johnny is a real relationship because at the start - you don't say that you hate him, because I've been told that you don't say that you hate someone - but we didn't like each other at all. But that's normal.
He was more than a rival. He was an ambitious young fella who wants to announce his arrival on the big stage and I'm there. Do I think I'm going to make it easy for this guy? You must be joking.
O'Gara was asked by Regan if it was the case that Sexton had basically annoyed him as a person, the former Munster out-half responded emphatically.
It most definitely was. It was the same perception of me when I was starting off. That this guy had a bit of a head on him. But that has to be, it's bread and butter if you want to survive in this game. It's the position that gets all the heat.
We'd never met in an Irish camp. What happened in the Munster vs Leinster game when Darce scored and I was on the ground and he roared into my face, he apologised for that afterwards. Once a fella does that [you move on]. If it's a real apology, yes. If it's a kind of lip service, no.
Spending time with a fella, you understand what he's about. It is true that there were days where... there was Rala, Mark Tainton, me and Johnny in a car and there wouldn't be a word spoken; that's not a great way to live your life - for anyone in the car.
Overtime the bad blood between them diminished to the point where they became friends - their time together at Racing Metro particularly helped.
The two also found common ground, their mutual crankiness and self-doubt.
Crankiness and I'd say mutual self-doubt. Johnny is crippled with self-doubt as well because he wants to keep producing in the future.
I know because I had great chats with him over Barry's Tea in Paris. That's when you really get to know a fella because you're on your own, there's two of you. Sometimes it's great because you actually get more out of the wives. If Jessica and Laura get talking then you're kind of, 'Oh, we're on to something here.'
For me it's interesting because he's under my care and I'm an Irish coach and he's the key in the team. I'm trying to get the best out of him and being happy is the most important thing in a person. If you're not happy then it's very difficult and it was very difficult for him because the club was in a mess.
You can listen to An Irishman Abroad on iTunes.
Picture credit: Brendan Moran / SPORTSFILE