Andy Murray was beaten by brother Jamie in the quarter-finals of the Cincinnati Masters, spelling the end of the two-time Wimbledon champion's dabble with doubles.
The siblings were facing each other for only the second time in their professional careers, and Andy and Feliciano Lopez went down 6-7 (5) 7-5 10-4 to Jamie and fellow Briton Neal Skupski.
"It was tough, not the most enjoyable match. The atmosphere kind of felt a bit flat on the court which I think is in some ways normal in those sorts of matches," Andy Murray told reporters.
"But it was fine, and I'm happy Jamie got through. You want to go out there and compete and play as well as you can, but you're not getting the same enjoyment out of serving an ace or hitting a great return as you might be in other matches.
"Obviously we tried to do our best but it wasn't enough today."
The defeat all but spells the end of Andy Murray's sojourn into doubles on the day he announced he would not play the men's or mixed events at the US Open later this month.
Having taken up doubles to feel his way back into top-level tennis following career-saving hip surgery, the 32-year-old Scot won the Queen's Club title with Lopez and enjoyed a run to the last 16 at Wimbledon in the mixed doubles with Serena Williams.
The former world number one will now concentrate on resuming his singles career at next week's ATP event in Winston-Salem, after losing on his return to singles 6-4 6-4 to Richard Gasquet in Cincinnati on Monday.
Just a couple of weeks after playing together in the doubles at the Citi Open, the Murray brothers faced off for the first time since their only previous meeting, in Montreal in 2015, where Jamie and John Peers beat Andy and Leander Paes.
Skupski, possibly feeling some pressure playing in such vaunted company, dropped his opening service game with a double fault to give Andy Murray and Lopez an early advantage.
But then Andy Murray's serve was broken for 4-4, with Lopez enduring a horror show as he dumped two simple volleys into the net and sent an overhead long.
Lopez got his act together in the tie-break and a Skupski volley floated wide to hand the Queen's champions the first set.
Some scintillating rallies enthralled an increasingly full Grandstand Court as the second set went with serve until, at 5-5, Lopez double-faulted on deciding point and Skupski served out to level the match.
In the match tie-break Lopez, who appeared to have tweaked a muscle in his serving arm, double-faulted twice to gift Jamie Murray and Skupski five match points.
Defeat was confirmed when Andy Murray netted a forehand as his brief dalliance with doubles came to an end.
