The Australian's belief at the time was that Verstappen was starting to be favoured by Red Bull and he was being pushed into more of a number two role.
The duo's controversial collision during the 2018 Azerbaijan Grand Prix, when Ricciardo ran into the back of Verstappen as the Dutch driver attempted to defend fourth place, only served to further undermine their relationship at the time.
After four years away, Ricciardo has returned to Red Bull as Third Driver to assist Verstappen and current team-mate Sergio Perez in preparation for grands prix.
Verstappen ‘carrying himself well' – Ricciardo
Asked by Speedcafe.com as to how welcoming Verstappen had been since meeting up again, Ricciardo said: “It's actually been really nice being back with the team, but also with Max.
“In the few years now I've spent outside of the team, I've seen him grow and mature, certainly as a driver, but I think also as an individual.
“Obviously there was the Baku clash but really, other than that – we were very competitive, of course – but I think we always had a very good personal relationship.
“We communicated as well over text and stuff so it's kind of just nice to see where we are.
“Obviously, since I left, he's become a two-time world champion, so to see his success and growth as well as a driver.
“But he's carrying himself really well and, honestly, he seems pretty unchanged, other than, you know, maturing as an individual.”
Ricciardo planning text upgrade chat
One of Ricciardo's key roles over the coming campaign will be to help develop the RB19.
The 33-year-old knows he will have to work hand in glove with Verstappen and Perez to ensure the car carries the ideal setup into each race weekend.
“Once I get into the heavier simulator work, I'm sure I'll start to be in contact more with Max and Sergio,” added Ricciardo.
“I'll text them and be like, ‘Guys, this is kind of what I felt. How do you feel about this?'
“Or ‘Is this kind of the direction you're looking for? Is this kind of the same weakness on track as maybe what I experienced today?'
“Or ‘Do you want me to develop a bit more in this area? Is this where I should maybe push the engineers or the sim team?'
“That'll be the stuff I will certainly communicate to them.
“If they come to me with things, I'm obviously happy to help and ultimately, just try to develop and make the whole team better.”