Former Presidents Bill Clinton and George W. Bush engaged in a lighthearted battle on social media following the release of Bush’s book, “41,” about his father.

Clinton and Bush, who have often appeared together promoting various causes, presided over the United States for nearly all of the 1990s and aughts, and there’s evidently no hard feelings for Clinton’s defeat of his father in 1992’s election. Clinton tweeted out a photo of himself reading Bush’s book, stating: “Received my copy of #41 by #43, George W. Bush. Touching tribute! #HowAreYouSTILLNotOnTwitter #PresidentialTweeters,” according to ABC News.

In fact, Bush does have a Twitter handle — @GeorgeWBush, but it is not in use: the George W. Bush Foundation has been holding the account since 2009, although the account is not verified and has not been used.

However, the 68-year-old Bush posts regularly on Instagram with 94 posts to date, and used that medium to respond to Clinton, who is also 68.

“Thanks 42! Hope you like the book about your pal, #41. #HowAreYouSTILLNotOnInstagram #PresidentialGrammers #BrotherFromAnotherMothe,” Bush wrote, posting a screenshot of Clinton’s tweet.

A spokesman for Bush said that while it may not be him who personally types out the caption, the posts are his own. A spokesman for Clinton responded to questions about his intentions to join Instagram with “the speculation is going to have to continue.”

Bush recently ribbed his predecessor in comments during an interview with Fox News’ Sean Hannity, according to Politico.

“Look, I’ll still like him [Bill Clinton], if Jeb — when Jeb beats Hillary,” he said while smiling. Asked if he was betting on that, Bush said that he was if Jeb Bush does decide to run, adding that “he’d be a great president.”