Pierre Gasly has admitted his surprise at getting the Red Bull call for 2019 to replace Daniel Ricciardo - while he found out the decision in just his pants.

The French driver will graduate from Toro Rosso to join Red Bull alongside Max Verstappen in its switch to Honda engines with Ricciardo making the shock decision to move to Renault.

After Ricciardo’s Renault deal was confirmed, two obvious candidates appeared in the shape of Gasly and fellow Red Bull-backed driver Carlos Sainz Jr who is currently on loan to Renault for this year.

But with Sainz announcing his move to McLaren for 2019, replacing two-time Formula 1 world champion Fernando Alonso, Gasly duly got the nod from the Red Bull bosses despite only moving into F1 as a full-time driver less than a year ago at the 2017 Malaysian Grand Prix.

Gasly concedes the call from Dr Helmut Marko, who confirmed he would be moving up to Red Bull, came as a surprise while he was enjoying the last week of his summer break in the South of France with his friends.

“There were a lot of emotions as well and I was just so shocked,” Gasly said in an interview with Red Bull following the announcement. “I didn’t really know what I was saying to my mates, so I jumped in the pool and celebrated with my mates and family.

“It was even more special to be there with them as we only really get to spend one week a year together. We try to see each other every year, but of course with the Formula 1 calendar it’s difficult to see them.

“So to get the news during that week when I was with them was even better. They’ve supported me every weekend from my karting days and as I was moving up through the series. Celebrating with them, they were just super happy for me as well, so it was a great moment.

“When Helmut started the call with me I was in my underwear... When the call ended I ran around the house shouting to my mates and they all jumped in the pool straight away!”

Gasly also brings a year of experience with Honda in F1, with Toro Rosso making the engine supplier switch at the start of this season, while the French driver’s relationship with the Japanese manufacturer flourished last year during his sole Super Formula campaign with Team Mugen.

“Working with Honda for the past two years certainly helps,” he said. “When I came to Super Formula we started to build up the relationship with them at that time. Then when I switched to Toro Rosso it was pretty good that Honda started the relationship with the team at the same time as me.

“Now next year Honda start with Red Bull, making the switch with me, it’s like I follow them with their next steps so it’s pretty cool.

“I know the way they communicate, the way they work. It’s beneficial and the experience of driving with them this year with their engine, I know their strengths, I know where they can improve, so for sure bringing that experience next year is always useful.”