Solange Knowles reportedly lashed out at Jay Z because he has failed to help boost her career.

The singer, 27, physically attacked her brother-in-law in an elevator at the Met Gala after-party in New York City on Monday night (05.05.14) because the rapper has reneged on repeated promises to work with her in the studio.

A source told the MailOnline: ''Solange is so angry because Jay Z promised to give her more help with her career and when she brought it up again the night of the gala, he told her he just didn't have the time to work with her in the studio. He hasn't kept his promise to help her.

''Jay keeps telling her to give him some time and he will sit down and write with her and then get her into the studio but he hasn't done it yet.''

Surveillance footage emerged yesterday (12.05.14) of Beyoncé's younger sibling hurtling towards Jay - real name Shawn Carter - in a lift in The Standard Hotel, while the 'XO' hitmaker watched on helplessly in the background.

Prior to the drama, Beyoncé, 32, and Solange were seen dancing up a storm on the dancefloor with supermodel Naomi Campbell, while the Jay, 44 - who has two-year-old daughter Blue Ivy with his spouse - ''hung back at one of the fireplace areas''.

However, it is believed the 'Holy Grail' hitmaker wasn't the only one to receive a telling off from Solange that night as she was reportedly seen yelling at fashion designer Rachel Roy earlier in the evening as well.