According to Screen Rant, Judd Nelson (John Bender from “The Breakfast Club”) appears as Chris McElroy in the episodes “Hookers, Hookers, Hookers” from Season 4 and “A Good Time in Central Africa” from Season 9.
McElroy is the ex-husband of Alan’s on-again, off-again squeeze, Lyndsey McElroy (Courtney Thorne-Smith), and is the father of her teenage son, Eldridge (Graham Patrick Martin). Chris contemplates reconciliation with his ex-wife during his first appearance — it was his fault they divorced in the first place, due to an affair. Alan is left in the dust, as they consider a second act for their marriage.
By the time Season 9 rolled around, Alan and Lyndsey are back together. When Chris shows up again, Alan believes that Chris is stalking him, inspiring great fear and panic in Alan. Naturally, he’s managed to misunderstand Chris’ intentions. All of this fear is ultimately for naught. Lyndsey and Alan end up engaged in the penultimate episode of “Two and a Half Men,” capping off an epic “Breakfast Club” cameo.