The Blues trio have all played a big part in Chelsea's opening matches of the 2019-20 campaign despite all three having been out on loan last season.
He told FATV: "It was after the Lille game. He didn't want to tell us before but I think he knew before the game.
"We'd just won, we're buzzing and the gaffer comes and grabs me, Fikayo and Mason and whispers 'you're all in the England squad'. We looked at each other and were buzzing. We hugged each other and made a Snapchat video."
Tomori, meanwhile, is part of a senior England squad for the first time, having previously been involved with the Under-21s, and he explained how he called his father to let him know the good news.
He said: "You don't really think: this is how I'm going to react when I get called up for England kind of thing, obviously the manager told me and I was kind of like 'oh'.
"Yeah [it was surreal], I remember I called my dad after. Obviously we won [against Lille] and he was like 'well done on the game' and I was like 'yeah dad, I'm going to get called up to the England squad'.
"He was like 'nah' and I just said 'yeah!' He asked how did I know and I just said the manager just told me. He just started shouting down the phone 'wheeeeey'.
"Obviously those are the kind of moments you never forget. I'm watching football most of the time with my dad. So I'm watching England with my dad, I'm watching Champions League with my dad, Match of the Day. So for him to share those moments with me, it's nice to do that."
Mount has been tipped to start against Czech Republic in Friday's Euro 2020 qualifier, while there could well be the opportunity for both Abraham and Tomori to feature in Prague, or in the meeting with Bulgaria on October 14.
The Three Lions are currently top of qualfication Group A and have won all four of their opening matches, scoring 19 goals and conceding just four in the process.