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Castlelake, L.P. confirmed it is considering a possible offer for British budget airline easyJet, sending the airline's stock up as much as 10% on Monday.

The Minneapolis-based investment firm said on May 29 that it was in early stages of evaluating a potential bid, and has not approached easyJet's board. In a follow-up announcement on June 1, Castlelake disclosed it already holds 16,241,494 ordinary shares of easyJet — roughly 2.14% of the airline's issued ordinary share capital — and said any offer would be valued at no less than 403.23 pence per share. At that minimum price, easyJet's total equity would be worth roughly £3.06 billion ($4.12 billion) — a premium of 1.3% over the 398 pence per share at which the stock closed on Friday, The Wall Street Journal reported.

EasyJet said it had not received any proposal from Castlelake and was not in any talks, according to The Wall Street Journal.

Under U.K. takeover rules, Castlelake must by June 26 either announce a firm intention to make an offer or declare that it does not intend to proceed. There can be no certainty that any offer will be made, the firm said.