The rumoured couple, who previously claimed they were just good friends, were spotted with their arms around each other as they watched the 'Hotel California' rockers perform at The Forum in Inglewood, Los Angeles.
The One Direction singer, 19, and the 'Keeping Up with the Kardashians' star, 18, who were introduced in November and have since enjoyed dinner dates in New York and London, as well as a skiing trip in California, were joined by the brunette model's half-sister Khloe Kardashian, 29, and her mother Kris Jenner, 58, according to the MailOnline website.
Fans also posted pictures of the pair looking very affectionate on Twitter, including one of the British star wrapping his arms around Kendall from behind and whispering in her ear.
But the duo were clearly hoping to keep their date under-wraps as they left the venue separately.
E! Chat show host Chelsea Handler also attended the gig with the group just days after Kendall played coy about Harry when she was interviewed by the comedienne on 'Chelsea Lately'.
A source previously revealed that the teen's older half-sisters Kim and Kourtney Kardashian are worried the 'Kiss You' hitmaker will break her heart.
The insider said: ''Kim, Kourtney and Khloe are super worried about baby sis, and keep warning her, 'Don't fall in love with Harry, he's going to break your heart'. But it's too late, Kendall told them, 'I'm already madly in love with Harry.' ''