Rapper tells crowd at show in New Jersey about his impending fatherhood and serenades his girlfriend

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Kanye West is to become a father, he announced in typically understated style on Sunday night – from the stage, in front of 5,000 fans in Atlantic City, New Jersey.

The hip-hop superstar stopped his set and asked the crowd to "make some noise for my baby mama right there", before serenading his girlfriend Kim Kardashian with the words "now you having my baby".

Kardashian's family – made famous by the reality show Keeping Up with the Kardashians – responded to the news with a barrage of tweets. Kim's sister Kortney tweeted: "Been wanting to shout from the rooftops with joy and now I can! Another angel to welcome to our family. Overwhelmed with excitement!"

Khloe, another sister, told the world: "I'm excited for Kanye and my sister! There's nothing like bringing life into this world! Let's keep Gods blessings coming!"

Kendall and Kyle Jenner – also sisters of Kim's – tweeted: "Whos excited about the KIMYE babbyyy?!", and "Congrats to this beautiful couple. I love you guys."

West's announcement came on the final night of a three-show run at the Ovation Hall at the Revel Resort in the seaside gambling town. The previous night West had embarked on a rant about a variety of subjects in which he said he would not attend next year's Grammy awards, following his failure to win the best album award this year. He also spoke of cancelling a world tour with Lady Gaga.