Ex-New Zealand schoolteacher Schmidt coached Sexton every day for three years at Leinster.
The moment Sexton joined Racing Metro and Schmidt stepped up to Ireland last summer though, that chain of command disintegrated.
Sexton's big-money French move dumped a whole new world of problems on Ireland, with Schmidt forced to concede the Irish Rugby Football Union had "lost control" of one of its chief assets.
The 26-year-old played 13 games in 11 weeks with Racing in the build-up to Ireland's autumn Guinness Series in Dublin.
He arrived injured for Ireland duty after tweaking his hamstring in France, then still being forced to sit on the bench for a 9-6 defeat at Biarritz.
That French muscle-flexing left the IRFU in no doubt that the reins are well and truly tied to the purse strings when Irishmen head abroad.
England's Aviva Premiership clubs are just as happy to pilfer top talent from the Celtic nations, Ospreys' Lions hooker Richard Hibbard's Gloucester deal the latest proof.
But the IRFU may just have found an unlikely English ally in the bid to offset the perils of star turns heading abroad.
London Irish are ready to live up to their name again after fresh investment saved the club from a future of uncertainty.
"We've got to become the fifth province for Ireland effectively," said the Exiles' Ireland scrum-half Tomas O'Leary.
Mick Crossan, the owner of waste management company Powerday, has taken the board helm at Irish, promising greater frontline and back-room investment for next season.
Irish reached a Heineken Cup semi-final in 2008 and a Premiership final in 2009 but have since floundered.
Not any more, according to their 24-cap half-back.
"Hopefully the club can strengthen the relationship with the IRFU again now," said O'Leary.
"If we can get a lot of Irish players over here that's only going to strengthen Irish rugby.
"Whether they are players coming out of school, players coming out of academies who don't make it at home or just guys who fancy a change.
"We'd be providing extra players eligible for Ireland, and playing at the top level too.
"So ultimately it's going to benefit the IRFU.
"Hopefully we can get a few high-profile players over the next few years; that would be great.
"And hopefully we can strengthen the relationship with the IRFU back home."
O'Leary won the Heineken Cup with Munster, and is among the few long-serving Limerick club men to seek gainful employment elsewhere.
But the 30-year-old half-back said life with the Exiles is purposely a home from home: now he has challenged the club to capitalise.
"That's the history and heritage of the club, it's the whole point," he said.
"Any Irishman coming over here to play is proud of their heritage.
"You chat to second generation Irishmen who are living over here, and they are really proud to support London Irish.
"It's really important we maintain that and strengthen that."
Livewire Wallabies back James O'Connor and Springbok World Cup winner CJ Van der Linde are the immediate fruit of Irish's boardroom shift.
Irish move into a state-of-the-art training facility next door to their long-term Sunbury base in the summer, and boss Brian Smith expects new recruits in management as well as squad.
O'Leary hopes the Aviva Premiership will start to take Irish seriously again.
He said: "Hopefully people will see that the club is ambitious, that we're not happy with where we are in the league.
"We're not happy with how we've performed over the last four or five years.
"Hopefully that perception will change and we have to match that ambition on the pitch with what's happening with the board.
"It's an exciting time for the club but essentially just because we have investors coming in and a new board it doesn't mean we're going to be a better team on Friday night.
"The challenge there short term is still for us to produce on the pitch.
"Moving to a new training ground and facility in the summer, maybe the board will change a few things in the background about how the club is run.
"They are going to invest in the squad and facilities and that's exciting going forward.
"The pressure is going to increase on us with the new board coming in: they are going to have their ideas and will want to see things changing."