The star receiver opened up on the blockbuster trade on the "KG Certified" podcast this week ... saying he was told about the potential deal during a Gatorade shoot ... and an hour later, #3 was gone.

"I ain't heard from Pete [Carroll] until later that night and John [Schneider] because they were probably busy with phone calls and everything," Metcalf said.

Of course, Metcalf and Wilson -- who was traded to the Broncos earlier this month in exchange for picks and players -- had great chemistry on the field. Last season, the two connected for 12 touchdowns.

Considering how well they clicked on the field, Metcalf says he didn't see the move coming.

"I never thought he was gonna leave Seattle" ... adding, "I was in just in shock because I didn't think it was gonna happen."

What also hit home for Metcalf -- the release of linebacker Bobby Wagner, who was with the 'Hawks for 10 seasons.

"So, my mind was like 'All right, Russ gone, what do I do?' Later that night, Bobby gets cut ... and me and Bobby -- that was my guy."

"When he left, that hurt," Metcalf added. "That was my big brother."

With all the offseason blows, Metcalf feels he has to step up more than ever ... and become a leader for the Seattle Seahawks.

"It's my time in Seattle, now. That's the way I look at it."

Metcalf was a 2nd-round pick out of the 2019 draft ... and quickly became a star in Seattle with his size and speed. In three seasons, he's logged in 3,170 receiving yards and 29 TDs.