Gasly, who is good friends with Ferrari driver Charles Leclerc and is in regular contact with Hamilton, says that the bombshell Formula 1 news of the seven-time champion's switch to Maranello did not catch him completely by surprise.
Speaking at the launch of Alpine's 2024 car at its Enstone factory on Tuesday, Gasly said it was his understanding that things had been bubbling away for quite some time.
"Obviously, he's been a long time with Mercedes, but I was aware of some talks with Ferrari," said Gasly.
"Ultimately, he's towards the end of his career. So it was either now or never.
"I think it was kept secret for quite a long time. I just wish him the best. Obviously, it's sort of exciting with the driver market, and all of you guys come with it, which is normal.
"But I think ultimately, for the sport, he is the most successful driver of all time joining a new project, a new challenge. I'm sure everybody will follow that very closely."
Gasly admitted that the Hamilton signing was not great news for Carlos Sainz, but said it was understandable what Ferrari had done.
Asked if the situation was fair on Sainz, Gasly said: "What's fair in F1, first of all? I think Carlos is a great driver. Lewis is a fantastic driver, the best of all time. So, on that side of things, I think there was an opportunity on both sides.
"I think Ferrari and Lewis took it together. Obviously, it leaves Carlos in a trickier situation. It's not easy."
Hamilton's Ferrari move has opened up a prime Mercedes seat for 2025, with the German manufacturer appearing to be in no rush to decide who takes it.
Gasly is aware that there could be a lot of movement in the driver market this year but said that should not distract him from the core task of producing his best performances on track.
"The approach coming into every single weekend is the same," he said. "It doesn't really matter whether there are seats for grabs or not.
"You've got to be smart in the way you race. You've got to be aggressive, which you are all the time. But knowing what's for grabs and maximising the chances you get, that doesn't really change."
He added: "I think my goal in F1 has always been clear. I want to fight at the front. That's why I came to Alpine a year and a half ago - because I want to be fighting for top positions.
"So, it hasn't changed my approach to Formula 1. I just turned 28. Basically, at my prime. I know I have some good years ahead of me, so it hasn't changed anything on my side."
