The 15-year-old Gauff has captivated Wimbledon after becoming the youngest player in the professional era to qualify for the main draw before beating Venus Williams and 2017 semi-finalist Magdalena Rybarikova to reach the third round.
Dart received a text from Clarke, saying he was switching partners ahead of the mixed doubles opening round on Thursday.
"Essentially due to the timing I wasn't able to find another partner in the time period available," Dart, who plays singles on Thursday against Brazilian Beatriz Haddad Maia, told the Daily Mail https://www.dailymail.co.uk/sport/tennis/article-7211103/Jay-Clarke-brutally-dumps-mixed-doubles-partner-Harriet-Dart-text-team-Cori-Gauff.html.
"I did ask a number of people but a lot of them were set up and that's it. I think you should ask Jay about his reasons, that's all I want to say."
Clarke said Gauff, known as Coco, had contacted him and asked him if he could partner her.
"I've known Cori for a few years now, we got in contact and she asked me to play," the Briton said. "That was tough, I had to let her know because I saw the pairs that had signed in, and I was (thinking) 'am I even going to get in?'"
"I think it's the worst decision I have had to make especially mid tournament. I didn't sleep too well the night before I played Noah (Rubin in a first-round singles match) but hopefully she understands why I did it. I'm sorry for her it happened."
Clarke lost to Roger Federer in a second-round singles match later on Thursday, after which he said he and Gauff had the same management company and had been to concerts together.
"She's with a management group. I'm with the same management group. Yeah, her agent spoke to my agent. We went to a few concerts last year with the company," he said.
"Yeah, so she's a really, really cool kid. She's got a really bright future."
Consolation for Dart, 22, was that she reached the third round of the singles with a 7-6(4) 3-6 6-1 win over Brazilian Beatriz Haddad Maia to set up a clash with world number one Ash Barty.
Asked about the switch after her victory, she told reporters: "I think that's in the past. Yeah, I think just got to look forward. I'm just concentrating on my singles."
Clarke and Gauff will face Robert Lindstedt and Jelena Ostapenko in the mixed doubles first round.
(Reporting by Rohith Nair in Bengaluru, editing by Ed Osmond)
