The Oscar-winning actress, 78, appeared as a guest star in the hit period drama alongside 49-year-old cast regular Coyle, and she cheekily admits she developed a "crush" on the actor despite their age difference.
When she confessed her saucy secret to the show's creator Fellowes, he mischievously organised for the pair to head out on a lunch date together.
MACLaine tells British magazine Seven, "I love doing Downton... I have kind of a crush on Brendan. He's quite mysterious. You don't really know what he's up to... I think (Fellowes) wanted to see if there were any cougaring (sic) sparks flying."