The singer, 32, and Kravitz , 37, were photographed together following a visit to Kravitz's hotel in London, where Styles was seen leaning into her Range Rover to kiss her.
The latest sighting of the pair, reported by The Sun on Tuesday, marks a major public display of affection between the pair and has intensified rumours about the status of their relationship after months of speculation.
Kravitz was seen wearing a beige trench coat and baseball cap featuring the word "Kiss" – merchandise linked to Styles' album Kiss All The Time. Disco, Occasionally album – which recently reached No 1.
An onlooker told The Sun: "Harry and Zoë look so in love – and she's got an enormous diamond on her ring finger.
"He is such a gent and led her to a waiting car before leaning in and giving her a kiss.
"When she left Harry waved her off. Zoë had a massive smile on her face.
"You couldn't miss the ring on her finger. It is absolutely huge."
The pair's public encounter follows earlier claims they had been staying in separate beds during their trip to London, despite being seen holding hands.
According to The Sun, Styles was observed dropping Kravitz at her hotel earlier this week before returning alone to his home, and then collecting her again the following morning.
The couple are said to have spent Christmas together at Styles' family home before travelling to the Bahamas for New Year.
An insider told The Sun: "Harry and Zoë saw in the New Year together in the Bahamas.
"This one is said to have been extra special and there has been talk amongst locals that a proposal did take place."
The Sun first reported Styles and Kravitz were dating in August, after they were seen together inside Rita's bistro in Soho.
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