Allen & Overy is advising The Bank of Tokyo-Mitsubishi UFJ Ltd. (BTMU) on its proposed $5.75 billion acquisition of a majority stake in Bank of Ayudhya Plc., Thailand's fifth-largest bank.

BTMU plans to purchase as much as 75 percent of the available shares in Bank of Ayudhya, which includes a 25.3 percent stake presently held by GE Capital International Holdings Corp. GE has already agreed to sell its holdings to BTMU.

Thai conglomerate Ratanarak Group controls the remaining 25 percent share of Bank of Ayudhya, and has no plans to sell. Instead it will partner with BTMU to run the bank, according to a statement by BTMU.

The deal is subject to regulatory approval but is expected to be completed in December.

The Allen & Overy team was led by Tokyo partner Simon Black and Bangkok partner Suparerk Auychai. Nishimura & Asahi is serving as Japanese counsel to BTMU. Sullivan & Cromwell Tokyo partner Keiji Hatano and New York partner Donald Toumey are advising on U.S. banking regulatory matters.*

GE is being represented by King & Wood Mallesons and local firm Thanathip & Partners.

It is the latest expansion into Southeast Asia by a Japanese bank. In May, Sumitomo Mitsui Financial Group Inc. announced it was acquiring a 40 percent stake in Indonesia’s PT Bank Tabungan Pensiunan Nasional Tbk for $1.5 billion. Japanese banks have been eagerly expanding abroad to counteract slow growth in their home market.

Email: tbrennan@alm.com.

*Updated, 7/8/13: This story has been updated to include the Sullivan & Cromwell partners advising Bank of Tokyo-Mitsubishi UFJ Ltd.