Betty (Draper) Francis’ lung cancer diagnosis in the penultimate episode of Mad Men (2007-2015) is a little on the nose. Cigarettes are almost worthy of a credit as series regular in the cast and some of the most famous scenes in the show revolve around Lucky Strike and Don’s open apology letter for selling them. But writing it off as that simple wouldn’t give the show or Matthew Weiner, its creator, enough credit. If anyone would get lung cancer, of course it would be Betty. (As Erin Gloria Ryan details for The Muse, we should have seen it coming.) From the first episode, Betty has always been Don’s best customer.

Don and Betty met when he was casting for a fur commercial. (This, incidentally, is echoed in an episode in the final season). Betty bought what Don was selling, the picture perfect life in the suburbs. That, like the smoking, caught up with Betty, too. First, she suspected Don’s infidelity, and then she uncovered his secret identity. Don was cheating, in every aspect of the word: sleeping with other women, using another man’s identity, and living an unearned life. Granted, Betty did get a divorce, but she never revealed Don’s secret. Betty moved on to a more authentic version of that life with Henry, but she always remained complicit with Don. They remain, in divorce, the handsome glamorous couple, even reuniting for a tryst in season six.

In the end, though, it is Don’s most notable professional achievement that catches up with Betty. In his open letter ad in the New York Times called “Why I’m Quitting Tobacco.” Don says, “For over 25 years we devoted ourselves to peddling a product for which good work is irrelevant, because people can’t stop themselves from buying it. A product that never improves, that causes illness, and makes people unhappy. But there was money in it. A lot of money. In fact, our entire business depended on it. We knew it wasn’t good for us, but we couldn’t stop.” This could just as easily describe Betty’s relationship with Don.

In true Betty style, she writes a letter to Sally, on Henry’s letterhead, giving Sally explicit instructions about how she wants her funeral service handled including a picture of the dress she wants to be buried in. Sally had said to Betty earlier that Henry wouldn’t understand the choice against treatment because he doesn’t understand that “you love the tragedy.”

Ultimately, wasn’t tragedy exactly what Don had been selling all along? Sally defies her mother’s wishes and tells Don in the finale, months after he left, that Betty is dying. This leads to a last tearful and tragic phone call with Don and Betty. Both are stripped down versions of their former selves – Don in jeans, racing cars in Utah, and Betty sick, weak, and without make-up. They say a lot to each other without saying much at all. Jon Hamm and January Jones play the scene with understatement and raw emotion, tears coming for both when Don says, simply, “Birdie…” and we all know it is their last good-bye.