Both players have gone on to become bonafide Premier League stars after Hull were relegated in 2017.
Centre-back Maguire was sold to Leicester and became a full England international during his two-seasons at the King Power.
Manchester United came calling last summer and stumped up £80m to make him the most expensive defender of all time.
The 27-year-old played every Premier League game this season as United finished in third-place and remain alive in the Europa League knockout rounds.
And Weir, a United academy graduate himself, says it has come as no surprise to see Maguire's ascension in world football.
Speaking to Tribalfootball.com, Weir said: "Honestly I'm not surprised because (Maguire) was probably one of the best players I played with at Hull.
"He was just a machine, I mean he's absolutely massive. He was so good on the ball, so I wasn't surprised. And he's a really nice guy, laid-back and chill, so I wasn't surprised at all."
Maguire and Robertson after Hull City were relegated to the Championship in 2017
Robertson has arguably been one of football's greatest success stories this century given his rise from Scottish non-league football to Anfield.
After leaving Queen's Park for Dundee United, Robertson was picked up by Hull in 2014.
Instead Robertson rightly stole Moreno's starting spot and never looked back, becoming a vital part of Liverpool winning the Champions League and Premier League over the past two seasons.
Asked about Robertson, Weir added: "To be fair he probably surprised me more (than Maguire). He told me in preseason he thought he might be going to Liverpool.
"We played golf together a bit, he's a real character. But when he told me, I was like bloody hell, will he start there?
"And obviously he's come on and is now one of the best left-backs in the world, so I probably didn't see that coming, but fair play. I'm really happy for him, he's a great lad."