Article 105

1. Any third party may, in accordance with the Implementing Regulations, intervene in opposition proceedings after the opposition period has expired, if the third party proves that
a) proceedings for infringement of the same patent have been instituted against him, or
b) following a request of the proprietor of the patent to cease alleged infringement, the third party has instituted proceedings for a ruling that he is not infringing the patent.

2. An admissible intervention shall be treated as an opposition.

Case Law:

IPPT20250925, EBA-EPO, G 2/24, Foreo v Beurer
[G 2/24] After withdrawal of all appeals, appeal proceedings may not be continued by a third party who intervened during the appeal proceedings in accordance with Article 105 EPC.  (Article 107 EPC, Article 105 EPC). The intervening third party does not acquire an appellant status corresponding to the status of a person entitled to appeal within the meaning of - Article 107, first sentence, EPC.