Conservative media personality Megyn Kelly plans to attend former President Trump's rally in Pittsburgh the night before the election and speak on his behalf.

Saying she "never expected" to be invited to stump for Trump, Kelly told her audience in a short clip posted on social media that during Monday night's event she will "explain to that crowd and beyond why I think it is absolutely essential he win this election."

"I have all sorts of reasons that won't come as any surprise to the people listening to this show," she said.

Kelly is the second leading conservative media pundit and former Fox News host to join Trump on the campaign trail.

The former president has sat for fireside chats and hosted campaign events with commentator Tucker Carlson, who has spoken on Trump's behalf and included the former president on a speaking tour this year.

Kelly and Trump have a complicated relationship that goes back years.

When Kelly was still at Fox in 2015, she famously pressed him on his comments about women during a GOP primary debate. Trump later attacked Kelly, saying she had "blood coming out of her eyes, blood coming out of her, wherever," during the episode.

Kelly has since said she and Trump have repaired their relationship, and today she uses her popular podcast and online commentary show to promote the former president and his allies.

She last week complained about Trump's controversial rally at Madison Square Garden, which she called too "bro-tastic" and warned could hurt Trump with women voters.