Miley is apparently "casually dating" the 26-year-old, who in 2011 past romanced actress Liv Tyler, 36. He is the photographer son of Rolling Stone magazine owner and chief editor, Jann Wenner.
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According to Radar, the star speaks to Theo "several times a day" and "talks about hot Theo is and how nice he is".
The publication also says Miley is so taken with her beau that she left her Bangerz New York launch party early on 8 October to be with him.
It also claims the flowers that arrived at the party for the 20-year-old were from Theo, not her other rumoured love interest, rapper Mike Will Made It.
Miley and her former love, 23-year-old Liam confirmed their Split in September after months of speculation.
Miley's rumoured new boyfriend Theo with Liv Tyler in 2011
They met on the set of The Last Song in 2010 and got engaged in May last year.
Earlier this year, the stars decided to postpone their nuptials. After delaying the wedding, Miley was spotted with her 3.5-carat Neil Lane engagement ring off and on. Then the rumour mill went into overdrive when she unfollowed her fiancé on Twitter.
The pair's last joint outing was in August, when they attended the LA premiere of Liam's latest film Paranoia.