Gore was a sore subject in conversations revealed Friday in hacked emails from Clinton's campaign chairman, John Podesta.
In an exchange released Friday, Clinton's top aides in November 2015 discussed Gore's public declaration he would not endorse Clinton's campaign, despite serving as her husband's vice president.
Top Clinton adviser Cheryl Mills sent a copy of an article on Gore's non-endorsement, to which aide Huma Abedin replied that they had been warned. Asked why the lack of endorsement after the Clintons endorsed his unsuccessful 2000 campaign by Mills, Abedin said there was a history.
"Well that was 16 years ago," she wrote. "Hard to put on email but there is no love lost in this relationship. Reminder that he also refused to endorse in 2008!!!"
"I know that's why i thought this time would be different," Mills replied.
"No its (sic) bad," Abedin wrote back.
Gore did endorse Clinton after the primary was wrapped up, and this month campaigned with her for the first time since 2000.
WikiLeaks has released emails daily over the past two weeks and has promised to do so into the future. US officials have said the releases bear the hallmarks of Russian meddling in the US election -- which WikiLeaks has denied.
It is impossible to verify the authenticity of the emails or the context, as WikiLeaks controls their release and the Clinton campaign has refused to confirm or deny any documents' authenticity.
The acrimony between Clinton and Gore has been well known since the White House years under Bill Clinton's administration, and before this month had last seen each other in 2014.
Since his failed campaign for president, Gore has been involved less in politics and has focused on his signature issue of global climate change. That was the focus of their joint campaign appearance in Miami, in the state that famously cost Gore the election.