Marry after extremely regrettable service (6)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

PAIR (as a verb = join together = marry) after the end letters (extremes) of R [egrettabl] E . A slightly loose definition: I’d think of “service” (as in a car’s annual service) as making sure it continues to work correctly, and “repair” as fixing it when it doesn’t. But there’s some overlap between the two I suppose.