Aluko rose through the ranks at Blues, spending over 10 years with his boyhood club, before then boss Steve Bruce, another celebrating victory over his former employers, allowed the forward to go out on loan to Aberdeen in 2007 prior to a permanent switch 12 months later.
And the 23-year-old thoroughly enjoyed his first return as he took full advantage of Birmingham's high defensive line to grab a well-taken brace and take his tally to eight goals for the season, with James Chester's third putting Hull firmly on course for their first win at Birmingham since 1970.
Ravel Morrison sparked a Blues revival before the break while Marlon King, another playing against a former club, bagged his 10th of the season 21 seconds into the second half to firmly make a game of things.
But the home side, subject to takeover speculation, could not find that crucial leveller as the fourth-placed Tigers held on to get back to winning ways.
Aluko should have opened his account for the afternoon after just six minutes.
The forward was sent clean through, with the home defence looking for offside, but his effort was well blocked by England starlet Jack Butland from a central position 12 yards out.
Aluko soon got a second chance, though, as he was sent clear again in the 14th minute and he made no mistake on this occasion, rounding Butland to finish coolly despite going to ground.
And the forward grabbed his and Hull's second 12 minutes later, again taking full advantage of Birmingham's high line to be set free and finish well.
Tigers goalkeeper Ben Amos saved well at the feet of Nikola Zigic but it was soon three-nil, Aluko turning provider this time as his inswinging corner was headed home by defender Chester.
Morrison bagged his first goal for Blues since his arrival on loan from West Ham, smashing home Zigic's knockdown to give the hosts hope before the break, with Tigers defender Abdoulaye Faye lucky not to then give away a penalty for handball.
If Blues finished the first half strongly then they started the second on fire, with a long ball going up towards Zigic, who headed down for King to score with just 21 seconds on the clock.
Aaron Mclean wasted a great chance to make the game safe in the 82nd minute before Birmingham threw everything at the Hull backline, ultimately to no effect in a dramatic finish.