Demi Lovato performs at Y100's Jingle Ball at the BB&T Center on Sunday, Dec. 17, 2017, in Sunrise, Fla. Picture: AP

American singer Demi Lovato has blasted former 'Celebrity Big Brother' star Perez Hilton, saying he's "irrelevant" in a series of scathing posts on social media.

The 'Sorry Not Sorry' singer appeared to take aim at the reality star in a thinly-veiled tweet, admitting it felt "so f***ing great" to make Perez watch her "kill it" on stage.

Without directly naming Perez, she tweeted: "The other night I got to sing SNS directly to one of USA's most notorious bullies. It felt so f***ing great.

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"That's what the song is all about!!! Sorry not sorry that you were in the audience watching me kill it. And btw - he's remaining nameless because he doesn't deserve the relevance that he doesn't have anymore (sic)"

Her blunt comments follow Perez's underwhelming review of her performance at the MGM Grand Garden Arena in Las Vegas on Saturday (03.03.18).

He wrote: "I am a Demi Lovato fan. She wasn't bad. She was better than before. I have nothing bad to say."

He later responded to Demi's tweets, cheekily referring to her 'Sorry Not Sorry' single as he attempted to put an end to the apparent feud.

Perez wrote on his website: "Demi Lovato thinks I'm irrelevant and wants to give me a little relevance by tweeting about me... Sorry I'm not sorry I said nothing but nice things about her and it. (sic)"

The night before Demi's MGM Grand Garden Arena show, she performed at The Forum in Inglewood, California, and fans got to witness an emotional moment when she invited former 'American Idol' star Rayvon Owen onstage.

Rayvon's boyfriend Shane Bitney Crone entered the stage via a trap door before getting down on bended knee to ask for Rayvon's hand in marriage.

Rayvon said yes and the audience cheered as the happy couple locked lips, and Demi, 25, ran over to give them a hug.

Speaking on stage, Demi said: "What some of you don't know is that these are two of my really close friends and I've gotten to watch Shane go through so much and come out on the other side ... such a strong person who's now found the love of his life. I'm so happy guys. I'm so f***ing happy."