Celtic tonight completed the signing of Scotland midfielder Paul Hartley from Hearts.
The midfielder, 30, passed a medical in Glasgow and signed a two-and-a-half-year contract, with Celtic having the option to extend his stay for a further 12 months.
The deal is thought to be worth just over £1million to Hearts, with Hartley's destination on transfer deadline day proving a surprise.
He had been expected to join Rangers, who were the first club to make their interest known, however Celtic met Hearts' asking price before their Old Firm rivals.
Celtic have made previous attempts to sign Hartley from Hearts, initially in 2004 and also last year, and will be delighted to have succeeded in adding him to their midfield squadron.
Hartley - who signed a new contract with Hearts last year - was missing from the Hearts squad for Saturday's Bank of Scotland Premier League game against Rangers.
Head coach Valdas Ivanauskas revealed afterwards that Hartley was omitted for 'football business' reasons, having already confirmed he was one of five players for sale just 24 hours before the trip to Ibrox.
He becomes Celtic's fourth signing of the month and will be reunited with his former Hearts captain Steven Pressley at Parkhead.
Pressley moved to Celtic the start of the month, following his release from the Tynecastle club in December.
Hartley sat alongside Pressley in a show of support as the 33-year-old revealed 'significant unrest' at Tynecastle in late October, a protest against owner Vladimir Romanov.
The other signings in January have seen Inverness Caledonian Thistle goalkeeper Mark Brown make a highly surprising move to the club to serve as back-up to Artur Boruc, while defender Jean-Joel Perrier-Doumbe arrived on a six-month loan deal from Rennes.