Jimmy Fallon had apologized on Twitter after Michelle Bachmann appeared on his "Late Night with Jimmy Fallon" show.

Story highlights

NEW: The NBC apology letter called the incident "unacceptable"

The candidate called for the network to apologize over the incident on Jimmy Fallon's show

A song with a derogatory title was played as Bachmann walked on stage Monday

Fallon apologized by Twitter on Tuesday

Washington CNN  — 

NBC has apologized to Rep. Michele Bachmann after the house band for “Late Night with Jimmy Fallon” played an inappropriate song during her appearance on the show Monday, CNN confirmed Thursday.

Bachmann received a letter Wednesday from Doug Vaughan, NBC’s senior vice president for special programs and late night, that apologized for what happened and called the incident “not only unfortunate but also unacceptable,” said Alice Stewart, the Republican presidential hopeful’s spokeswoman.

According to Stewart, the letter also said the show’s band, which played the song “Lyin’ Ass Bitch” by Fishbone as Bachmann first appeared on stage, was “severely reprimanded.”

“She accepted the apology,” Stewart told CNN Thursday.

Bachmann also spoke to Fallon Wednesday and had a “nice conversation,” said Stewart, who described the late night host as “remorseful” and “a class act.”

Fallon had offered an apology via Twitter on Tuesday, but Bachmann then called for an official apology from NBC.

The controversy started Monday when the Minnesota congresswoman walked out to greet Fallon on stage, and the show’s band, The Roots, played the Fishbone song.

Bachmann admitted being oblivious to the slight, telling Fox News on Wednesday that she “wasn’t aware of it at all.”

She insisted the treatment she received through the song amounted to “sexism,” and she added that it “wouldn’t be tolerated if it was Michelle Obama and shouldn’t be tolerated for a conservative woman, either.”

Still, she said, “I’d love to go back again.”

Some of Bachmann’s ire was directed toward the drummer of Fallon’s house band, Ahmir “Questlove” Thompson.

“If that song had been played for Michelle Obama I have no doubt that NBC would’ve apologized to her and likely they could’ve fired the drummer or at least suspended him. None of that happened from NBC and this is clearly a form of the bias on the part of the Hollywood entertainment elite,” Bachmann said.

The song choice appeared to be intentional. Prior to Bachmann’s arrival on stage, the band’s drummer, Questlove, tweeted during the show: “Aight late night walkon song devotees: you love it when we snark: this next one takes the cake. ask around cause i aint tweeting title.”

Despite the song choice, the interview was amicable, with Bachmann and Fallon trading jokes.

On Tuesday, Fallon tweeted: “I’m honored that @michelebachmann was on our show yesterday and I’m so sorry about the intro mess. I really hope she comes back.”

The band also issued a statement saying “the performance was a tongue-in-cheek and spur-of-the-moment decision.”

Stewart said Thursday that Bachmann recognized that Fallon “had no idea this happened.”

Fallon has invited Bachmann back on the show, Stewart said, adding that no date was set but “she would prefer to pick her opening music next time.”

CNN’s Tom Cohen contributed to this report.