Sienna Miller's new boyfriend Rhys Ifans is tipped to replace actor David Tennant in hit British sci-fi series Doctor Who. The Notting Hill star is considered "one of the front runners" to succeed the famous Timelord role after Tennant steps down in 2009. A source tells British newspaper the Daily Express, "It's felt that Rhys would bring very different dimensions to the role maverick, slightly menacing Doctor, perhaps more in the Tom Baker mould."