Grimace and Uncle O’Grimacey are welcoming the Shamrock Shake back to restaurants nationwide on Monday, Feb. 10

McDonald's is leaning on customers' nostalgia for its McDonaldland characters to spur sales of its Shamrock Shake. The company said Tuesday that Grimace will reunite with his Iris

McDonald’s is bringing back its beloved Shamrock Shake with the help of an old friend. The minty green milkshake will return to restaurants on Monday, Feb. 10 — and the chain’s Uncle O’Grimacey character is returning after a decades-long hiatus to help kick off the annual “Shamrock Season.”